Behavioral Ecology - recent issues

Female tungara frogs vary in commitment to mate choice

Baugh, A. T., Ryan, M. J. — Thu, 12 Nov 2009 07:49:22 PST

Mate choice studies most often examine female preferences based on population responses, thus potentially overlooking individual differences in behavior. Moreover, such studies typically use invariant stimulus conditions to infer preferences. By using population responses and static stimulus presentations, it is difficult to thoroughly understand the complexity of the mate choice process, including variation present between individuals. Here, we investigated phonotactic mate choice behavior in female túngara frogs (Physalaemus pustulosus) in response to temporally dynamic presentations of male advertisement calls. We tested females on repeated trials to examine individual differences and found considerable variation in the extent to which females update their mate choice decisions. Females in our study were bimodally distributed and thus broadly classified as either committed or uncommitted to an initial mate approach. We compared body condition measures of females differing behaviorally and determined that females with larger residual body masses were more committed to initial mate choices than less massive individuals, despite the fact that all females were in reproductive condition and field collected in amplexus. Our results suggest that anuran phonotaxis, once considered to be a highly stereotyped behavior, is more complex and variable than previously thought.

Food quality affects search strategy in the acellular slime mould, Physarum polycephalum

Latty, T., Beekman, M. — Thu, 12 Nov 2009 07:49:22 PST

When searching for resources, organisms can increase the efficiency of search and exploitation behavior by using information about the quality of a current resource patch in their decision making. The search strategy used by an organism can in turn affect its performance in different landscapes. Here we examine the effect of resource quality on 2 foraging decisions: how much time to allocate to explore the environment for new resources and what search strategy to use during exploration. We used the slime mould Physarum polycephalum as our model system. Physarum polycephalum is an amoeboid organism that forages as a flowing mass of pseudopods. We quantified the search pattern of plasmodia after engulfment of food of 6 different qualities. Food quality had a significant, positive effect on how long plasmodia waited before resuming search behavior and on how long it took to abandon food disks. Food quality had a positive effect on fractal dimension, indicating that the amount of localized search performed by plasmodia increased with food quality. Our results suggest that increasing food quality results in a shift from extensive to intensive search. Next, we examined foraging performance in landscapes with different patch structures. Plasmodia in correlated landscapes (half the patches contained only high-quality food, half contained only low-quality food) gained more weight than plasmodia foraging in noncorrelated landscapes (patches contained both high- and low-quality food disks). Our results show that food quality affects exploitation and search behavior and that both behaviors influence foraging performance in different landscapes.

Individual behavior and survival: the roles of predator avoidance, foraging success, and vigilance

Sansom, A., Lind, J., Cresswell, W. — Thu, 12 Nov 2009 07:49:22 PST

Variation in antipredation behavior should translate into variation in survival. Effective general defenses, such as predator avoidance, decrease the likelihood that an individual is attacked and should therefore reduce selection on behaviors that enhance probability of escape on attack. Escape behaviors become important if animals cannot avoid attack. We investigated the relative effects of avoidance and escape enhancing behaviors on the survival of juvenile redshanks, Tringa totanus, over 2 winters. We predicted that avoidance behavior should be the primary behavioral correlate of survival, but when forced, by starvation risk, into areas where risk of attack is much higher, behaviors that reduce risk of capture once attacked should also promote survival. We found that reducing exposure to attack was most important for increasing survival and that increased vigilance and foraging success rate only increased survival for individuals that spent more time in high-risk areas. Use of the high-risk area and survival varied between years, suggesting that variation in starvation risk (i.e., colder winters) may provide a mechanism for selection on "capture-reducing" antipredation behaviors to be maintained because predator avoidance, the most effective antipredation behavior, is not then possible.

Male and female crickets use different decision rules in response to mating signals

Leonard, A. S., Hedrick, A. V. — Thu, 12 Nov 2009 07:49:22 PST

Males that produce conspicuous mating signals may attract competitors in addition to sexually receptive females. In many species, for example, females use male calls to locate and choose mates and males respond to competitors’ signals by modulating signal production or changing location, thereby escalating or decreasing competition. Do these different receivers make decisions using male signals in the same way? We compared how male and female field crickets (Gryllus integer) made decisions to approach male calls differing in calling bout length, a heritable trait known to play an important role in female mate choice. When offered a simultaneous choice between playbacks, both males and females preferred calls with long bouts to those with short bouts. When presented with calls in isolation, however, only females preferred long-bout calls. Females thus appear to use an internal standard to evaluate calls, whereas males apparently compare the relative attractiveness of alternatives. We also found that males assess calls in relation to their own competitive potential by testing 2 hypotheses that make different predictions regarding variation in male responses to competitor signals. We found no support for the satellite male hypothesis, as unattractive males did not preferentially approach female-preferred calls; in support of the aggressive displacement hypothesis, males likely to win contests preferentially approached the female-preferred call. Our work demonstrates that even though the sexes process the same information, different mechanisms of reproductive success (mate location vs. mate attraction) can result in sex differences in the perception and use of conspecifics’ signals.

Paternity in the classical polyandrous black coucal (Centropus grillii)--a cuckoo accepting cuckoldry?

Muck, C., Kempenaers, B., Kuhn, S., Valcu, M., Goymann, W. — Thu, 12 Nov 2009 07:49:23 PST

In birds, a high degree of paternal care is expected to correlate with a relatively low frequency of extrapair paternity. If females seek extrapair copulations, they may lose fitness because their partners may reduce paternal care. Conversely, a high degree of paternal care might give females extra opportunities to pursue extrapair copulations, whereas their mates are occupied with offspring care. The aim of this study was to investigate paternity in the classically polyandrous African black coucal. In this sex-role reversed species, males intensively invest in offspring care of altricial young. However, the likelihood of extrapair fertilizations through stored sperm or extrapair copulations seems very high because females lay up to 3 clutches for up to 3 males each. Using 9 novel, highly polymorphic microsatellite loci developed for black coucals, we determined paternity of 127 chicks from 35 nests. Of these, 18 chicks (14.2%) from 13 broods (37.1%) were not fathered by the social male. Black coucals thus have the highest average rate of extrapair paternity reported for any classically polyandrous species. Extrapair young were the result from both extrapair copulations with males outside the female's group of social mates and stored sperm from previous mates. We suggest that males were unable to effectively guard their females to prevent extrapair paternity due to 1) the dense habitat they live in and 2) the onset of incubation before clutch completion.

The effects of wind on trap structural and material properties of a sit-and-wait predator

Liao, C.-P., Chi, K.-J., Tso, I-M. — Thu, 12 Nov 2009 07:49:23 PST

Numerous terrestrial invertebrates use secretions produced by themselves to build prey traps. Potentially, the structural as well as material properties of such constructions will reflect adaptations to wind disturbances, but most relevant studies only focus on trap structural characteristics. In this study, we examined how wind disturbances affected the structural and material properties of prey traps constructed by a sit-and-wait Araneae predator. We first compared web structures and major ampullate (MA) silk properties of 2 Cyclosa spider species inhabiting seashores and forests to see whether these properties reflected the habitat-specific wind disturbances these spiders experienced. The MA silks of the seashore-dwelling Cyclosa mulmeinensis were significantly thicker and contained higher percentage of glycine and lower glutamine. Congruent with such amino acid variation pattern were higher ultimate tension and breaking energy of C. mulmeinensis MA silks. However, despite that this species’ silks were relatively glycine rich and glutamine poor, they also showed greater extensibility. Compared with webs built by Cyclosa ginnaga, those built by C. mulmeinensis were composed of fewer drag-reducing silk threads but were stiffer. In a laboratory manipulation, MA silk amino acid composition and diameter did not differ between C. mulmeinensis receiving different levels of wind. However, those receiving persistent wind disturbances built smaller webs composed of fewer but stronger MA silks to reduce drag and prevent the web from damage. Orb web spiders inhabiting areas with different levels of wind disturbances exhibit variation and plasticity in structural and material properties of prey traps. Furthermore, the silk property plasticity does not have to involve alterations of amino acid composition.

Coral bleaching and habitat degradation increase susceptibility to predation for coral-dwelling fishes

Coker, D. J., Pratchett, M. S., Munday, P. L. — Thu, 12 Nov 2009 07:49:23 PST

Climate-induced coral bleaching frequently leads to declines in the abundance and diversity of coral-associated fishes, though the proximate causes of these declines are largely unknown. In this study, we show that coral-dwelling damselfishes associated with bleached and dead coral hosts are more susceptible to predation compared with fishes associated with healthy coral colonies. Although the predator (Pseudochromis fuscus) actively avoided both bleached and recently dead corals, they were almost twice as likely to strike at prey associated with the stark white colonies of bleached corals. These results suggest that coral-dwelling fishes are much more conspicuous against the bleached-white background, increasing their susceptibility to predation. Direct estimates of predation rates in aquaria were 33% and 37% on bleached and recently dead coral colonies, respectively, compared with 25% on healthy coral colonies. However, predation rates were highest (42%) on algal-covered corals, reflective of colonies that have further degraded after bleaching. We argue that increased susceptibility to predation may contribute to declines in abundance of coral-dwelling fishes after host coral bleaching. Even if predation does not cause increased in situ mortality, it is likely that increased exposure to predators will provide significant motivation for coral-dwelling fishes to vacate bleached coral hosts.

Reproductive energetics in free-living female chimpanzees (Pan troglodytes schweinfurthii)

Murray, C. M., Lonsdorf, E. V., Eberly, L. E., Pusey, A. E. — Thu, 12 Nov 2009 07:49:23 PST

Mammalian females generally carry the bulk of reproductive costs. They gestate for relatively long periods of time and provide the majority of parental care for dependent offspring. For this reason, many studies have examined how females deal with the energetic costs of reproduction. Here, we examine the influence of reproductive state on activity budgets, diet quality, and sociality in free-living female chimpanzees (Pan troglodytes) at Gombe National Park, Tanzania. After controlling for dominance rank, we found that pregnant and lactating females consumed higher quality foods than nonpregnant, nonlactating females. However, pregnant females also traveled less. This result did not reflect differences in sociality, as the pregnant female group sizes included in our analyses were comparable to those in other reproductive categories.

Persuasive companions can be wrong: the use of misleading social information in nutmeg mannikins

Rieucau, G., Giraldeau, L.-A. — Thu, 12 Nov 2009 07:49:23 PST

Animals sample their surrounding environment to collect information, which can be obtained personally or by tracking the behavior of others (i.e., social information). Although social information appears to be generally advantageous, it can also be detrimental and may even conflict with personal information. We tested the effect that the strength of social information, and ultimately its persuasiveness, can have on an animal’s decision to use it or not by conducting an experiment using single nutmeg mannikins (Lonchura punctulata), which were offered a foraging choice after observation of videos of feeding or nonfeeding conspecifics. The persuasiveness of social information was amplified by increasing the number and changing the behavior of conspecifics that had previously been seen feeding at 1 of 2 feeders. In addition, we modulated the certainty of an individual’s personal information. Some birds had prior experience of a marked feeder always containing easily accessible food, whereas other birds experienced that this was only the case in half of the trials. Our results show that animals provided with sufficiently persuasive social information will tend to reduce the weight of even highly reliable personal information. This provides the first experimental evidence consistent with the propagation of informational cascades in nonhuman animals, which have been invoked to explain market crashes in economics or panic rushes in human crowds.

Environment-dependent use of mate choice cues in sticklebacks

Heuschele, J., Mannerla, M., Gienapp, P., Candolin, U. — Thu, 12 Nov 2009 07:49:23 PST

Human-induced environmental changes alter terrestrial and aquatic ecosystems worldwide. This influences also evolutionary processes, such as sexual selection, by constraining mate choice and mate competition. Organisms often use multiple cues in mate choice, with different cues indicating the same or different benefits. Because the assessment and information content of cues can vary with environmental conditions, changes in the environment could alter mate choice. Here we determined if increased phytoplankton turbidity influences the relative use of olfactory and visual cues in mate choice in the three-spined stickleback Gasterosteus aculeatus. In a mate choice experiment, we found that females relied more on visual than olfactory cues in clear water. However, in turbid water, the pattern was the opposite with olfactory cues being more important than visual cues. Interestingly, mate preferences based on visual and olfactory cues did not agree, which suggests that human-induced environmental change could shift mate choice. This could influence the direction and target of sexual selection and have further consequences for the viability of the population under the new conditions.

The educated prey: consequences for exploitation and control

Bischof, R., Zedrosser, A. — Thu, 12 Nov 2009 07:49:23 PST

There is convincing evidence that, in addition to improving their responses to natural predators, animals can also learn from their experience with human exploiters or man-made kill and capture devices. Despite its potential importance, the effect of improved defences to general exploitation (including human harvest) has received little attention so far. To address this void, and to link with practical considerations for management of exploited populations, we develop a general exploitation model with separate states for naive and educated individuals. We then evaluate and illustrate the relevance of acquired/improved defences for the dynamics of exploited populations and their management by applying the modeling framework to 2 management spheres with global scope, harvesting of wildlife populations, and control of invasive species. The strength of the predicted influence of educating prey on population and exploitation dynamics was positively affected by the intensity of exploitation and initial survival of naive individuals and negatively by the speed of life history of the target populations. We also demonstrate that the potential for response loss can lead to counterintuitive results with respect to effort and yield. Our model provides a framework for exploring adaptive behavior in the context of exploitation and for making both qualitative and quantitative predictions.

Female cooperation in plug formation in a spider: effects of male copulatory courtship

Aisenberg, A., Eberhard, W. G. — Thu, 12 Nov 2009 07:49:23 PST

One of the strongest indications that cryptic female choice is an evolutionary phenomenon of general importance is the widespread existence of male courtship behavior during copulation. It has been presumed that such copulatory courtship functions to induce female reproductive behavior that favors the male's reproductive interests, but this function has seldom been demonstrated. Here, we examine the possible effects of male copulatory courtship in the spider Leucauge mariana (Tetragnathidae) on whether a female will aid the male in forming a copulatory plug, thus reducing the chances that future mates will be able to inseminate her. Greater numbers of 2 behavior patterns by the male during copulation, rhythmic pushing on the female's legs with his front legs, and repeated short insertions with his genitalia were associated with increased chances that the female would cooperate in plug formation. This confirms that these behavior patterns do indeed function as courtship.

Courtship effort is a better predictor of mating success than ornamentation for male wolf spiders

Shamble, P. S., Wilgers, D. J., Swoboda, K. A., Hebets, E. A. — Thu, 12 Nov 2009 07:49:23 PST

Female mate choice decisions are often based on a variety of male characteristics, some of which may reflect male quality via condition-dependent trait expression. Here, we explore the condition dependence of a male secondary sexual trait in a wolf spider and examine its influence on female mate choice. In the wolf spider Schizocosa uetzi, mature males possess a multimodal courtship display (visual + seismic) in which they slowly raise and lower their dark colored forelegs. Foreleg color is highly variable among S. uetzi males with respect to both total amount and darkness. Using diet manipulations in conjunction with color quantifications, we demonstrate condition-dependent foreleg color. High-nutrient diet males had significantly higher body condition indices and possessed more and darker foreleg color than low-nutrient diet males. However, using multiple mate choice designs, we were unable to demonstrate a female preference for male foreleg color. Using both single and 2-choice mating designs as well as using females from a range of ages, we found that copulation success was consistently independent of male foreleg color. Instead, we found courtship intensity to be the only aspect of male courtship that influenced copulation success—males that copulated displayed more leg raises per second than those that did not copulate.

Odor preference in house mice: influences of habitat heterogeneity and chromosomal incompatibility

Nunes, A. C., Mathias, M. d. L., Ganem, G. — Thu, 12 Nov 2009 07:49:23 PST

Theory predicts that when maladaptive hybridization occurs assortative mating preference should evolve. Moreover, habitat characteristics can influence quality of mates that is an important criterion in mate choice. Here we ask how chromosomal compatibility and differences in habitat quality might shape preference for odors of the opposite sex in the house mouse. Our study model is composed of 2 chromosomal races and their narrow hybrid zone that occur in habitats of different qualities. We performed 2-way choice tests during which opposite sex urine mixtures of each race were presented to mice from the 2 races and the hybrid zone. Differential investigation of the odor sources indicated both preference and that the odors differed. The results show that the 2 races carry distinct odors and, irrespective of the race they belonged to, males preferred odors of females from the race occurring in habitats of lower quality (hereafter, race B), whereas females preferred odors of males from the race occurring in habitats of better quality (hereafter, race A). Further, preference in the hybrid zone was for race B odors, which differed significantly from that displayed by the 2 races (i.e., for race A odors). The relative influences of geography, ecology, and chromosomal compatibility are discussed, thus leading us to propose that habitat differences might play the most important role in shaping signal divergence and preference in this system.

Limited kin discrimination abilities mediate tolerance toward relatives in polyembryonic parasitoid wasps

Segoli, M., Keasar, T., Harari, A. R., Bouskila, A. — Thu, 12 Nov 2009 07:49:23 PST

We modeled the possible effect of limited kin discrimination on larval aggression in polyembryonic wasps. In these organisms, each egg divides clonally to produce several genetically identical embryos inside an arthropod host. If more than one egg is laid inside a host (superparasitism), several clones compete for the host resources. In some species, a proportion of embryos develop into sterile soldier larvae that attack competitors inside the host. Soldiers were shown to attack according to relatedness, with higher levels of aggression toward less related individuals. Yet, the tolerance of soldiers toward nonclonal relatives is puzzling, given the intense competition for host resources, which is not offset by inclusive fitness. Using a decision tree model, we looked for conditions that justify soldier tolerance. We assumed 2 possible strategies for a soldier: A tolerant soldier does not attack a competing clone and an aggressive soldier attacks any clone that it identifies as a competitor. We calculated the expected payoffs of each strategy under different conditions of relatedness and probabilities for discrimination errors. The model predicts that when discrimination ability is perfect, a soldier should attack any competitor, regardless of relatedness. However, when discrimination ability is restricted, soldiers should switch from aggression to tolerance with increasing relatedness to competitors. The model demonstrates that limited discrimination abilities may shift the threshold of relatedness required to induce tolerance. This may apply to other systems of kin recognition that are prone to discrimination errors.

Are bird species that vocalize at higher frequencies preadapted to inhabit noisy urban areas?

Hu, Y., Cardoso, G. C. — Thu, 12 Nov 2009 07:49:23 PST

Urban environments have become an increasingly important part of the world's ecosystems, and the characteristics that enable animals to live there are not fully understood. A typical urban characteristic is the high level of ambient noise, which presents difficulties for animals that use vocal communication. Urban noise is most intense at lower frequencies, and, therefore, species vocalizing at higher frequencies may be less affected and thus better able to inhabit urban environments. We tested this hypothesis with within-genera comparisons of the vocalization frequency of 529 bird species from 103 genera. We found that species occurring in urban environments generally vocalize at higher dominant frequency than strictly nonurban congeneric species, without differing in body size or in the vegetation density of their natural habitats. In most passerine genera with low-frequency songs, which are more subject to masking by noise, minimum song frequency was also higher for urban species. These results suggest that species using high frequencies are preadapted to inhabit urban environments and that reducing noise pollution in urban areas may contribute to restore more diverse avian communities.

Current brood size and residual reproductive value predict offspring desertion in the burying beetle Nicrophorus vespilloides

Ward, R. J.S., Cotter, S. C., Kilner, R. M. — Thu, 12 Nov 2009 07:49:23 PST

Life-history theory suggests that offspring desertion can be an adaptive reproductive strategy, in which parents forgo the costly care of an unprofitable current brood to save resources for future reproduction. In the burying beetle, Nicrophorus vespilloides, parents commonly abandon their offspring to the care of others, resulting in female-only care, male-only care, brood parasitism, and the care of offspring sired by satellite males. Furthermore, when there is biparental care, males routinely desert the brood before larval development is complete, leaving females behind to tend their young. We attempted to understand these patterns of offspring desertion by using laboratory experiments to compare the fitness costs associated with parental care for each sex and the residual reproductive value of the 2 sexes. We also tested whether current brood size and residual reproductive value together predicted the incidence of brood desertion. We found that males and females each sustained fecundity costs as a consequence of caring for larvae and that these costs were of comparable magnitude. Nevertheless, males had greater residual reproductive value than females and were more likely than females to desert experimental broods. Our results can explain why males desert the brood earlier than females in nature and why female-only care is more common than male-only care. They also suggest that the tipping point from brood parasitism or satellite male behavior to communal breeding (and vice versa) depends on the value of the current brood relative to residual reproductive value.

Learned conspecific mate preference in a species pair of sticklebacks

Kozak, G. M., Boughman, J. W. — Thu, 12 Nov 2009 07:49:23 PST

Sexual isolation between species often depends on preferences for conspecific mates. Recent models suggest that whether conspecific preference is determined genetically or learned will affect the process of speciation: Learned conspecific preferences might make speciation more likely. However, we understand little about how often and for which taxa, conspecific preferences are learned. Some species learn conspecific preference by imprinting on conspecifics; others learn from experience with heterospecifics. Even when one sex learns conspecific preference, the other may not. We tested whether conspecific mate preference is learned through social experience in males and females from 2 three-spined stickleback species that show strong sexual isolation (benthics and limnetics: Gasterosteus spp.). We reared fish with either mostly conspecifics or mostly heterospecifics and measured how this experience affected conspecific preference. In both sexes, experience enhanced conspecific mate preference but the sexes differed in the outcome. Females learned to prefer their own species through experience with conspecifics; males learned to discriminate through experience with heterospecifics. We also found species differences in the effect of social experience related to differences in sociality. Our results suggest that learned conspecific mate preference may have facilitated rapid speciation in the post Pleistocene radiation of sticklebacks.

Prevalence of avian influenza and sexual selection in ducks

Hegyi, G., Moller, A. P., Eens, M., Garamszegi, L. Z. — Thu, 12 Nov 2009 07:49:23 PST

Investigations of avian influenza have so far focused on the global circulation and conversion of virus strains and showed that wild waterfowl and especially ducks represent the reservoir and source of virus strains that can become highly pathogenic in domestic species. Information is largely missing regarding the routes of transmission between individuals and the species of concern for transmission. Moreover, evolutionary comparative studies only considered ecological factors and ignored other potential determinants of virus transmission. Such determinants include the mating strategies of hosts because links between sexual selection and parasites are well known. Here, we show that morphological adaptations associated with copulation frequency in both male and female hosts strongly explain differences in low-pathogenic influenza prevalence among wild duck species. Prevalence is negatively related to male phallus length and female vaginal complexity, traits that evolved due to sexual conflict over forced copulations. This pattern suggests a hitherto unrecognized transmission route of the virus via copulation and subsequent mother–offspring transfer. Due to a relationship between forced copulations and the expression of white wing covert patches, male covert patch expression and sexual dichromatism in covert patch expression are positively related to influenza prevalence. Our results suggest that the arms race between male and female reproductive tracts had epidemiological consequences. Our findings further suggest that morphological correlates of sexual selection in ducks, including conspicuous plumage ornamentation, could be robust clues to identify high-risk host species during the large-scale monitoring of avian influenza.

Sophisticated early life lessons: threat-sensitive generalization of predator recognition by embryonic amphibians

Ferrari, M. C.O., Chivers, D. P. — Thu, 12 Nov 2009 07:49:23 PST

The ability to develop effective antipredator responses early in life should be strongly promoted by natural selection. Recent work has shown that embryonic amphibians can learn to recognize predators even before they hatch. Here, we showed that embryonic woodfrogs, Rana sylvatica, learned the danger level associated with a predator prior to hatching and generalized their learned recognition to other similar predators with which the woodfrogs lacked experience. Embryos exposed to salamander odor (SO) paired with injured tadpole cues learned to recognize the salamander Ambystoma tigrinum, but those exposed to SO paired with well water did not. When we increased the concentration of alarm cues to which embryos were exposed, tadpoles showed stronger response to salamander cues. In addition, the tadpoles generalize their learned response to the odor of closely related newts Cynops pyrrhogaster but not Xenopus frogs. In accordance with the Predator Recognition Continuum Hypothesis, the ability to generalize was dependent on the threat level of the predator. Our results highlight the sophistication of learned responses to predators by embryonic amphibians and stress the need for studies in other taxa.

How depth alters detection and capture of buried prey: exploitation of sea turtle eggs by mongooses

Leighton, P. A., Horrocks, J. A., Kramer, D. L. — Thu, 12 Nov 2009 07:49:23 PST

Predators are an important source of mortality for animals that lay their eggs in buried nests. We asked how depth alters the process of predation for buried prey. We outlined a general model of predation risk where depth may alter both prey detection and subsequent capture: deeper prey are detected less often because the strength of olfactory cues decreases with burial depth and, once detected, are further protected by the costs of digging. Using this framework, we examined how burial depth influenced egg predation for critically endangered hawksbill sea turtles (Eretmochelys imbricata) by introduced mongooses (Herpestes javanicus) in Barbados. We tested the effects of nest depth on detection and subsequent predation using observational data on hawksbill nests over a 2-year period and an experiment with artificial nests. For both real and artificial nests, depth had little effect on nest detection by mongooses, but once detected, shallower nests were much more likely to be preyed on. Mongooses appear to use depth-invariant surface cues to detect nests but increase digging persistence in response to olfactory cues. We argue that excavation cost is an important but overlooked mechanism protecting deeply buried resources. For reptiles with buried nests, the relationship between depth and predation risk leads to important predictions about how changes to nesting habitat or the predator community will affect egg survival and offspring sex ratio. More generally, identifying the mechanisms by which burial depth protects prey is essential for understanding how resource burial strategies evolved and are maintained in predator–prey systems.

Courtship song's role during female mate choice in the field cricket Teleogryllus oceanicus

Rebar, D., Bailey, N. W., Zuk, M. — Thu, 12 Nov 2009 07:49:23 PST

Sexual signals consist of multiple components, each of which can contribute to mating decisions. Male field crickets use 2 acoustic signals in the context of mating: a calling song that attracts females from a distance and a courtship song that follows once a female makes physical contact with a male. The function of courtship is unclear because females have already chosen and approached a particular male based on his calling song. Using the field cricket Teleogryllus oceanicus, we tested whether females evaluate the attractiveness of males based on their courtship song irrespective of other male qualities. In a tournament-style assay, females chose males based on elements of their courtship song and preferred males with longer courtship songs that had a higher duty cycle (more sound per unit time). Courtship song was also highly repeatable not only within a bout but also between days in the presence of different females. Additionally, we manipulated the attractiveness of males to females by surgically silencing males and broadcasting playbacks of artificially constructed courtship songs. When we broadcast a preferred song model during courtship by previously nonpreferred males, females showed greater attraction, and vice versa. Courtship song may be particularly important in systems with satellite males that do not produce long-range signals because it gives females their only opportunity to evaluate potential mates.

Familiarity breeds contempt: effects of striped skunk color, shape, and abundance on wild carnivore behavior

Hunter, J. S. — Thu, 12 Nov 2009 07:49:23 PST

Multicomponent aposematic warning signals are generally accepted to function as a deterrent to predatory attacks; however, the relative importance of specific visual cues used by wild predators to recognize defended animals is poorly understood. Here, I use naturally and reciprocally colored taxidermy models of striped skunks (Mephitis mephitis) and gray foxes (Urocyon cinereoargenteus) to explore the impact of aposematic coloration and body shape on the behavior of wild mammalian predators. Models were baited, and all visiting species were recorded with remote video cameras at 10 wilderness sites in California, USA. I found that mammalian predators not only approached black-and-white models more hesitantly than gray-colored models but also reacted negatively to skunk-shaped models, suggesting that predators may generalize noxious qualities to both skunk coloration and skunk shape. This study also found an effect of skunk abundance on animal behavior with predators less likely to visit black-and-white models and more hesitant in their approach to skunk-shaped models at sites with greater skunk abundance. These findings suggest that prior experience and the frequency with which aposematic prey are encountered in a landscape are important predictors of predator avoidance of defended prey.

Mate choice based on complex visual signals in the brook stickleback, Culaea inconstans

Ward, J. L., McLennan, D. A. — Thu, 12 Nov 2009 07:49:23 PST

In species with complex courtship, females often have the opportunity to assess multiple male cues during mate choice. Depending on the strength and form of the coevolutionary relationships between male traits and female preferences, geographic variation in signal complexes can result in a variety of mate choice scenarios ranging from partial to complete positive assortative mating. Using mate choice trials, we investigated the relationship between intrapopulation female biases for complex visual signals and interpopulation mating dynamics in 2 populations of brook stickleback, Culaea inconstans, from distinct mitochondrial DNA genetic lineages. Our results showed that courtship effort is the primary visual criterion of mate assessment in this species; females from both lineages exhibited directional preferences for increased behavioral vigor. In contrast, male nuptial color intensity and body size had little influence on female choice decisions. Interpopulation divergence in male traits was not strongly correlated with divergence in female preferences, producing asymmetric patterns of assortative mate choice across the lineage divide. We compare female preferences for male visual traits in C. inconstans with other members of the Gasterosteidae and suggest that mate assessment differs substantially between stickleback species.

Why are females ornamented? A test of the courtship stimulation and courtship rejection hypotheses

Chan, R., Stuart-Fox, D., Jessop, T. S. — Thu, 12 Nov 2009 07:49:23 PST

Female ornamentation was initially thought to reflect genetic correlation with the more elaborate male trait. However, this cannot explain female-specific ornamentation, such as the conspicuous coloration displayed by females of many species during breeding. Females may exhibit distinctive, reproductive coloration to 1) advertise receptivity and stimulate male courtship or 2) advertise nonreceptivity when gravid to reduce male courtship, harassment, and potentially costly copulations. We tested both hypotheses in the Lake Eyre dragon lizard (Ctenophorus maculosus) by quantifying female coloration, using spectroradiometry and a model of lizard color perception, and male and female behavior across the female reproductive cycle. Females develop bright orange coloration on their throat and abdomen during the breeding season, whereas males remain cryptically colored. The onset of orange coloration was associated with enlarging follicles, acceptance of copulations, and escalation of male courtship. Rather than fading once females were no longer receptive, however, the intense orange coloration remained until oviposition. Furthermore, despite maximal coloration associated with nonreceptivity, males persisted with courtship and copulation attempts, and females increased rejection behaviors comprising lateral displays and flipping onto their backs (to prevent forced intromission), both of which emphasize the conspicuous ventrolateral coloration. These apparently costly rejection behaviors did not reduce male harassment but did decrease the frequency of potentially costly copulations. These results suggest that 1) males do not determine female receptivity based on coloration alone and 2) the potentially costly rejection behaviors may have evolved to reduce the direct costs of mating.

Cleaning in pairs enhances honesty in male cleaning gobies

Soares, M. C., Bshary, R., Cote, I. M. — Thu, 12 Nov 2009 07:49:23 PST

A recent game theoretic model akin to an iterated prisoner's dilemma explored situations in which 2 individuals (the service providers) interact simultaneously with the same service recipient (the client). If providing a dishonest service pays, then each service provider may be tempted to cheat before its partner, even if cheating causes the client's departure; however, a theoretical cooperative solution also exists where both partners should reduce cheating rates. This prediction is supported by indirect measures of cheating (i.e., inferred from client responses) by pairs of Indo-Pacific bluestreak cleaner wrasses Labroides dimidiatus. Here, we examine how inspecting in pairs affects service quality in Caribbean cleaning gobies Elacatinus spp. We measured dishonesty directly by examining the stomach contents of solitary and paired individuals and calculating the ratio of scales to ectoparasites ingested. We found that the propensity to cheat of females and males differed: females always cleaned relatively honestly, whereas males cheated less when cleaning in pairs than when cleaning alone. However, overall, the cleaning service of single and paired individuals was similar. Our results confirm that cleaners cooperate when cleaning in pairs; however, our findings differ from the specific predictions of the model and the observations on L. dimidiatus. The differences may be due to differences in mating systems and cleaner–client interactions between the 2 cleaner fish species.

Female American goldfinches use carotenoid-based bill coloration to signal status

Murphy, T. G., Rosenthal, M. F., Montgomerie, R., Tarvin, K. A. — Thu, 12 Nov 2009 07:49:23 PST

Interest in female ornamentation has burgeoned recently, and evidence suggests that carotenoid-based female coloration may function as a mate-choice signal. However, the possibility that females may signal status with coloration has been all but ignored. Bill coloration of female American goldfinches (Spinus tristis) changes seasonally, from dull gray in winter to bright orange in the breeding season. We conducted a series of aviary experiments in the breeding season to examine the signaling role of female bill color during both intra- and intersexual contests as well as during male mate choice. We tested for status signaling by examining whether caged females and males avoided feeding adjacent to female taxidermic models as a function of the model's bill color, which was experimentally augmented or dulled. We tested for a mate signaling function by giving captive males a choice between 2 live females with experimentally altered bill colors. Females avoided feeding near model females with colorful bills, but males showed neither avoidance of nor preference for females with more colorful bills. These results indicate that the female's carotenoid-based bill coloration signals status during competitive interactions and suggest that female bill color does not function as a mate-choice signal. This represents the first experimental evidence that a carotenoid-based coloration of females functions to mediate contest competition over food.

Importance of internal pattern contrast and contrast against the background in aposematic signals

Aronsson, M., Gamberale-Stille, G. — Thu, 12 Nov 2009 07:49:23 PST

Aposematic color patterns that signal prey unprofitability are suggested to work best when there is high contrast within the animal color pattern or between the animal and its background. Studies show that prey contrast against the background increases the signal efficiency. This has occasionally been extended to also explain the presence of internal patterns. We used domestic chicks, Gallus gallus domesticus, to investigate the relative importance for avoidance learning of within-prey pattern contrast and prey contrast against the background. In a series of trials, birds were first trained to avoid artificially made aposematic mealworms that were plain red or red with black stripes, and to discriminate them from palatable brown mealworms, on either a red or a brown background. Second, we investigated how the birds generalized between striped and nonstriped prey. The chicks showed faster avoidance learning when the basic color of the aposematic prey (red) contrasted with the background color (brown). However, there was no similar effect of internal pattern contrast. The generalization test showed a complete generalization between the nonstriped and the striped prey. We conclude that contrasting internal patterns do not necessarily affect predator avoidance learning the same way as shown for prey-to-background contrast in aposematic prey.

Changing philosophies and tools for statistical inferences in behavioral ecology

Thu, 12 Nov 2009 07:49:23 PST

Recent developments in ecological statistics have reached behavioral ecology, and an increasing number of studies now apply analytical tools that incorporate alternatives to the conventional null hypothesis testing based on significance levels. However, these approaches continue to receive mixed support in our field. Because our statistical choices can influence research design and the interpretation of data, there is a compelling case for reaching consensus on statistical philosophy and practice. Here, we provide a brief overview of the recently proposed approaches and open an online forum for future discussion (https://bestat.ecoinformatics.org/). From the perspective of practicing behavioral ecologists relying on either correlative or experimental data, we review the most relevant features of information theoretic approaches, Bayesian inference, and effect size statistics. We also discuss concerns about data quality, missing data, and repeatability. We emphasize the necessity of moving away from a heavy reliance on statistical significance while focusing attention on biological relevance and effect sizes, with the recognition that uncertainty is an inherent feature of biological data. Furthermore, we point to the importance of integrating previous knowledge in the current analysis, for which novel approaches offer a variety of tools. We note, however, that the drawbacks and benefits of these approaches have yet to be carefully examined in association with behavioral data. Therefore, we encourage a philosophical change in the interpretation of statistical outcomes, whereas we still retain a pluralistic perspective for making objective statistical choices given the uncertainties around different approaches in behavioral ecology. We provide recommendations on how these concepts could be made apparent in the presentation of statistical outputs in scientific papers.

Trait duplication by means of sensory bias

Rodriguez, R. L. — Thu, 12 Nov 2009 07:49:23 PST

Alternative foraging tactics and risk taking in brook charr (Salvelinus fontinalis)

Farwell, M., McLaughlin, R. L. — Tue, 15 Sep 2009 01:11:11 PDT

Recently emerged brook charr (Salvelinus fontinalis) foraging in still-water pools along the sides of streams tend to be sedentary, feeding from the lower portion of the water column (sitting and waiting), or active, feeding from the upper portion of the water column (active search). Individuals exhibiting intermediate behavior are observed less frequently. We assessed the perceptual, energetic, and locomotor bases of the individual differences in foraging tactics by testing whether an individual's activity while searching for prey in the field was linked to its willingness to take risks, resting metabolic rate (RMR), and swimming capacity. Proportion of time an individual spent moving during prey search was quantified in the field, the individual was captured, and willingness to take risks (field), resting oxygen consumption (lab), and locomotor ability (lab) were measured. Individuals that spent a lesser proportion of time moving in the field took longer to exit from a dark tube into an unfamiliar field environment, and delayed their exit times more in response to a novel object, than did individuals that spent a greater proportion of time moving in the field. Proportion of time spent moving in the field was unrelated to resting oxygen consumption and swimming capacity measured in the laboratory. Dispositions in foraging behavior and risk taking early in life could influence encounter rates with novel prey and habitats, which are important steps in the initial stages of resource polymorphisms.

Larger colonies do not have more specialized workers in the ant Temnothorax albipennis

Dornhaus, A., Holley, J.-A., Franks, N. R. — Tue, 15 Sep 2009 01:11:11 PDT

Social insects are distinguished by their extraordinary degree of cooperation and the complexity of their group organization. However, a high proportion of individuals (often >50% at any one time) in a social insect colony tend to be inactive. It has been hypothesized that larger colonies can afford such inactivity because of efficiencies gained through stronger division of labor. We quantify the degree to which colonies of different sizes exhibit division of labor, and what proportion tends to be inactive, in the ant Temnothorax albipennis. Colony size neither influenced individual specialization nor overall division of labor in this species and larger colonies did not show a higher proportion of inactive workers. Interestingly, small colonies seemed to rely more on a small number of high-performance workers: the proportion of work performed by the single most active worker is significantly higher in smaller colonies for several tasks. More research is needed to resolve when and how colony size affects collective organization and division of labor in insect colonies.

Food limitation increases aggression in juvenile meerkats

Hodge, S.J., Thornton, A., Flower, T.P., Clutton-Brock, T.H. — Tue, 15 Sep 2009 01:11:11 PDT

Both the rate and severity of sibling aggression are predicted to be higher when food availability is low. Although there is now good evidence that food availability influences sibling aggression in facultatively siblicidal species, where aggression commonly results in the death of a competitor, little is known about the proximate causes of aggression in nonsiblicidal species, where aggression rarely results in serious injury. Here, we investigated patterns of aggression between juvenile meerkats (Suricata suricatta), a species where littermate aggression is common, but never lethal. We show that the frequency of aggression between littermates increased when rainfall and helper number, both predictors of the amount of food available to pups, were low. Short-term feeding experiments demonstrated that reducing pup hunger by provisioning them before a foraging session significantly reduced their frequency of aggression in comparison to unfed controls. There was no evidence that offspring sex or weight influenced either the rate at which pups were aggressive, or which littermates they were aggressive to. These results suggest that food availability is an important factor affecting the severity of aggressive competition between offspring, even in the absence of lethal aggressive attacks.

Vigilance and predator detection vary between avian species with different visual acuity and coverage

Tisdale, V., Fernandez-Juricic, E. — Tue, 15 Sep 2009 01:11:11 PDT

Interspecific variations in avian visual systems have been suggested to influence antipredator strategies, yet little empirical evidence exists on how morphological and ecological factors associated with visual properties can constraint predator detection. We investigated antipredator responses (predator detection probabilities and vigilance behavior) in 2 species with different visual properties (European starlings, Sturus vulgaris, have higher acuity and wider blind areas at the rear of their heads than house sparrows, Passer domesticus) in relation to distance to the predator, body posture, and head orientation. Visual acuity may affect the distance at which a predator is detected; while the size of the blind area may influence the body postures and head orientation with the highest predator detection probabilities. Distance to the decreased predator detection probabilities of house sparrows (lower acuity) but not those of European starlings. Certain body postures and head orientations, influenced both species despite the interspecific differences in visual field configuration. Times allocated to scanning were similar, but European starlings had longer head-up scan bouts likely to enhance scanning coverage, whereas house sparrows had higher head-up scan rates probably to reduce the length of interscan intervals. We discuss alternative interpretations; however, our findings suggest that sensory configurations may limit the effectiveness of some antipredator strategies under certain ecological conditions, which has implications for understanding the evolution of different behavioral mechanisms that reduce predation risk.

Adaptive learning in the foraging behavior of the predatory mite Phytoseiulus persimilis

Rahmani, H., Hoffmann, D., Walzer, A., Schausberger, P. — Tue, 15 Sep 2009 01:11:11 PDT

Arthropod learning in the context of food acceptance and choice is commonly assumed to be adaptive but documentation of the adaptive value is scarce and lacking for true predators. We examined learning in juveniles of the predatory mite Phytoseiulus persimilis, which has a feeding preference for herbivorous spider mites but may use conspecific larvae as alternative prey. Adult predator females that had experienced conspecific larvae as prey during their juvenile phase attacked conspecific prey earlier than naïve predator females did. Shorter latency to attack of adult females did not depend on the length of exposure to alternative prey in the juvenile phase (24 h or whole juvenile phase). Experience decreased the predation rates of adult females but enhanced their survival chances when feeding on the alternative prey. The suggested proximate cause for enhanced survival of experienced females was greater energetic efficiency in foraging as compared with naïve females. Experience resulted in faster prey recognition and acceptance (indicated by shorter latency to attack) increasing prey profitability, and optimized daily predation rates. Ultimately, juvenile learning allows P. persimilis to better cope with shortage of the innately preferred spider mite prey.

Age-related reproductive performance in the parental burying beetle, Nicrophorus orbicollis

Trumbo, S. T. — Tue, 15 Sep 2009 01:11:11 PDT

Age-related improvements in reproductive performance have been explained by the selection, constraint, and restraint hypotheses (increased performance related to greater effort and a declining residual reproductive value). Using a laboratory population of the burying beetle, Nicrophorus orbicollis, 6 measures of performance were assessed. Consideration of the selection and constraint hypotheses was minimized by reducing mortality to near zero and comparing reproductive outcomes of equal-sized females with equivalent mating and breeding experience. Young and old females were provided a resource for breeding (mouse carcass) and were confronted by a potentially infanticidal intruder (young or old) after offspring were present in the nest. Younger females were more likely to experience a brood failure and were slower to oviposit eggs. Younger intruding females also were less likely to usurp a carcass from a resident female. Age, however, did not affect any measure of reproductive performance once a female had a brood. There were no differences between young and old females in the number and mass of offspring in original or replacement broods, or in the probability of successfully defending offspring against an intruder. In a follow-up experiment with smaller carcasses, there was, again, no significant difference in the ability of young and old females to defend their brood. In N. orbicollis, the reproductive restraint observed in younger females appears to inhibit the initiation but not the continuance of reproduction. The usefulness of the residual reproductive, targeted reproductive effort and the maturational limits hypotheses to explain age-related variation in reproductive performance are discussed.

Cryptic female choice by female control of oviposition timing in a soldier fly

Barbosa, F. — Tue, 15 Sep 2009 01:11:11 PDT

There is substantial evidence that cryptic female choice (CFC) is present in numerous taxa. Several mechanisms have been proposed for CFC; however, we only have experimental evidence for a few of them. Female control of oviposition timing is a potentially widespread mechanism of CFC, but it has never been experimentally demonstrated. The aims of this study are to test 2 critical predictions of the hypothesis that CFC through control of oviposition timing occurs in the soldier fly Merosargus cingulatus: 1) to determine if M. cingulatus females are less likely to oviposit immediately after mating when the male does not perform copulatory courtship than when he does and 2) to determine if failure to immediately oviposit by the female results in lower reproductive success for the male she just mated with. To answer the first question, I compared the oviposition behavior of females that mated with control males versus females that mated with manipulated males that could not perform copulatory courtship. I showed that M. cingulatus females fail to oviposit immediately after copulation when males do not perform copulatory courtship. To answer the second question, I showed that there is last male sperm precedence in M. cingulatus. Because the last male to mate fertilizes most of the female's eggs, a male will benefit when females oviposit immediately after mating with him and before remating with another male.

Individual quality and reproductive effort mirrored in white wing plumage in both sexes of south polar skuas

Tue, 15 Sep 2009 01:11:11 PDT

It is well established that female choice may lead to sexual selection on quality-revealing ornaments in males. However, in many species, both sexes display conspicuous characters, which may reflect individual quality and condition. We examined the correlations between measures of individual condition, reproductive performance and variation in size and whiteness of white wing patches in both sexes of the south polar skua (Catharacta maccormicki). Females with a whiter patch had a lower mean clutch size and higher survival, and males with whiter patches had higher immune responses against the injected immunogen tetanus. Birds with a larger white patch, on the other hand, had a higher mass loss, and females with large white patches laid larger eggs and had reduced survival probability. Thus, variation in 2 measured aspects of the wing patches in the south polar skua seems to mirror a gradient of reproductive investment strategies; from 1) reduced reproductive investment, better immune defense, and higher survival in birds with more intensely white wing patches to 2) high reproductive investment but survival costs in birds with larger patches.

Evolution and life-history correlates of female song in the New World blackbirds

Price, J. J. — Tue, 15 Sep 2009 01:11:11 PDT

Female song is much more prevalent in tropical than in temperate songbirds but, we know surprisingly little about the evolutionary origins of this striking latitudinal difference. Here I reconstruct the evolution of female song in the New World blackbird family (Icteridae) and compare historical changes in this trait to changes in several other life-history characters: social mating system, nesting pattern, and migratory behavior. Reconstructions using both parsimony and maximum likelihood methods show that female song has been lost repeatedly in this clade and that tropical ancestors with frequent female song almost invariably were monogamous, had dispersed nest sites, and were nonmigratory. Losses of female song were not consistently associated with changes in any single life-history characteristic across the family, but rather appear to have occurred for different reasons in different lineages, including the evolution of migration in the oriole genus (Icterus), the evolution of brood parasitism in the cowbirds (Molothrus), and the evolution of polygynous, colonial breeding in the oropendolas (Psarocolius, Gymnostinops) and caciques (Cacicus). These results support previous suggestions that the prevalence of female song in the tropics is largely explained by the life-history traits associated with tropical habitats.

Flexible cuckoo chick-rejection rules in the superb fairy-wren

Langmore, N. E., Cockburn, A., Russell, A. F., Kilner, R. M. — Tue, 15 Sep 2009 01:11:11 PDT

Recognition of brood parasitic cuckoo nestlings poses a challenge to hosts because cues expressed by cuckoos and host young may be very similar. In theory, hosts should use flexible recognition rules that maximize the likelihood of rejecting cuckoo nestlings while minimizing the risk of rejecting their own young. Our previous work revealed that female superb fairy-wrens Malurus cyaneus often abandoned nestling cuckoos and that the presence of a single chick in the nest was 1 trigger for abandonment because fairy-wrens also sometimes abandoned a single fairy-wren chick. Here we use a combination of 20 years of observational data, a cross-fostering experiment, and a brood size reduction experiment to determine the basis for individual variability in the chick-rejection rules of superb fairy-wrens in response to parasitism by Horsfield's bronze-cuckoos Chalcites basalis. We show that the decision to abandon a single chick is based on integration of learned recognition cues and external cues. Experienced females were relatively more likely to abandon a single cuckoo chick and accept a single fairy-wren chick than naive females. Breeding experience therefore facilitates the ability to make an accurate rejection decision, perhaps through learned refinement of the recognition template. In addition, fairy-wrens modified their rejection threshold in relation to the presence of adult cuckoos in the population, becoming more likely to abandon single nestlings with increasing risk of parasitism. By using these flexible rejection rules, female superb fairy-wrens are more likely to defend themselves successfully against exploitation by the cuckoo and are less prone to mistakenly reject their own offspring.

Remotely sensed productivity, regional home range selection, and local range use by an omnivorous primate

Willems, E. P., Barton, R. A., Hill, R. A. — Tue, 15 Sep 2009 01:11:11 PDT

Remote sensing of the environment has proved an invaluable tool to the study of animal ecology at continental to regional scales. Here, we investigated the utility of a remotely sensed index of plant productivity (the normalized difference vegetation index [NDVI]) at a much finer spatial scale to account for the range use of an omnivorous primate (the vervet monkey: Cercopithecus aethiops) foraging in a multipredator environment. Vervet monkey home range location suggested that the animals prefer areas with elevated productivity and reduced seasonality as indexed by simple NDVI metrics. Within the annual home range area, monthly NDVI values were linearly related to field measurements of leaf cover and quadratically associated with vervet monkey food availability. Temporal variation in parameters of local range use could subsequently be expressed in terms of local NDVI: Monthly averaged day journey length showed a second-order polynomial response, and the amount of time the monkeys spent on the ground increased with group size whereas linearly decreasing with monthly NDVI. The first finding signifies a behavioral response to food availability, whereas the latter is interpreted as an antipredatory response to changes in habitat visibility, associated with leaf cover. As a spatially explicit and temporally varying measure of habitat structure and productivity, the NDVI thus offers considerable scope for studies of animal behavioral ecology not only at broad spatiotemporal scales but also at a much finer grained level of analysis.

Female choice for optimal combinations of multiple male display traits increases offspring survival

Lancaster, L. T., Hipsley, C. A., Sinervo, B. — Tue, 15 Sep 2009 01:11:11 PDT

Females commonly incorporate information from more than 1 male trait when making mating decisions, which may increase their ability to choose high-quality males. Assessment of multiple male traits may also incur increasing costs of time and/or energy and should therefore provide an adaptive advantage over females that do not exhibit such complex mating decisions. Although this benefit has been assumed/concluded in previous mate choice studies, it has rarely been empirically verified with female fitness data. Here we show that female side-blotched lizards (Uta stansburiana) that assess males for optimal trait combinations of throat color (a polymorphic social signal) and dorsal patterning (a polymorphic antipredator trait) recruit more offspring to the next adult generation. Specifically, females preferred males with a barred dorsal pattern, but only when males were yellow throated (signaling a sneaker strategy in males). Females mated to sires with both these traits experienced high rates of progeny survival to adulthood, via inheritance of favorable genetic combinations from sires (indirect benefits). Previous results suggest that this is because barredness confers crypsis primarily in yellow-throated lizards and not in lizards with alternative throat colors. Together, these results support the hypothesis that female preference for multiple, interacting male traits is an adaptive response to complex patterns of natural selection on offspring, such as correlational selection on unlinked traits. Our results provide new evidence for an adaptive advantage to females that exhibit complex mating-decision rules and suggest that one advantage lies in reducing deleterious recombination of genes for traits that, only in specific combinations, enhance fitness.

Carotenoid-based status signaling by females in the tropical streak-backed oriole

Tue, 15 Sep 2009 01:11:11 PDT

In many tropical bird species, both males and females maintain elaborate plumage traits. Although there is considerable evidence that many male plumage traits function as status signals that convey information about fighting ability, less is known about status signaling in females. We tested whether the carotenoid-based orange breast coloration of the female streak-backed oriole (Icterus pustulatus pustulatus) signals status during territorial interactions. To do this, we simulated territorial intrusions using taxidermic models and compared the roles of the sexes within pairs during territorial defense directed toward different types of simulated intruders. Females were more territorial than their mates during the breeding season, whereas males were more territorial than their mates in the nonbreeding season, contrary to patterns seen in studies of temperate zone birds. The coloration of simulated female intruders also influenced territorial responses: When presented with color-augmented female models, females responded with greater intensity than their mates, whereas the intensity of defense was similar for both sexes when presented with average-colored female models. The greater female response to more colorful intruders suggests that females perceive more ornamented females as greater threats to their territorial tenure or to their pair bond. These results are consistent with the hypothesis that female carotenoid-based coloration signals status in this species.

Queen reproductive state modulates pheromone production and queen-worker interactions in honeybees

Kocher, S. D., Richard, F.-J., Tarpy, D. R., Grozinger, C. M. — Tue, 15 Sep 2009 01:11:11 PDT

The mandibular glands of queen honeybees produce a pheromone that modulates many aspects of worker honeybee physiology and behavior and is critical for colony social organization. The exact chemical blend produced by the queen differs between virgin and mated, laying queens. Here, we investigate the role of mating and reproductive state on queen pheromone production and worker responses. Virgin queens, naturally mated queens, and queens instrumentally inseminated with either semen or saline were collected 2 days after mating or insemination. Naturally mated queens had the most activated ovaries and the most distinct chemical profile in their mandibular glands. Instrumentally inseminated queens were intermediate between virgins and naturally mated queens for both ovary activation and chemical profiles. There were no significant differences between semen- and saline-inseminated queens. Workers were preferentially attracted to the mandibular gland extracts from queens with significantly more activated ovaries. These studies suggest that the queen pheromone blend is modulated by the reproductive status of the queens, and workers can detect these subtle differences and are more responsive to queens with higher reproductive potential. Furthermore, it appears as if insemination substance does not strongly affect physiological characteristics of honeybee queens 2 days after insemination, suggesting that the insemination process or volume is responsible for stimulating these early postmating changes in honeybee queens.

Should females prefer males with elaborate nests?

Lehtonen, T. K., Wong, B. B.M. — Tue, 15 Sep 2009 01:11:11 PDT

It is widely assumed that when males alone are responsible for nest building, nest characteristics should reflect the quality of its owner and that the nest itself should be an important cue in female choice. This, however, does not always have to be the case if, for example, nest attributes are an unreliable reflection of male quality. Here, we investigate whether females should prefer nest characteristics in a small marine fish, the sand goby, Pomatoschistus minutus. Previous findings suggest that female sand gobies prefer males that possess well-built nests (based on the amount of sand piled on top). It was unclear, however, whether females chose males based on the quality of the nest per se or some other, correlated quality of the builder. In the current study, we found conflicting evidence of whether males in good condition are able to bring a greater percentage of eggs to the hatching stage. In a field investigation, we also found that the relationship between body condition and the degree of nest construction was temporally unstable. Furthermore, when we experimentally disentangled nest quality from other male traits, we showed that females did not prefer to spawn with males that had the most elaborate nests. Together, these results suggest that females do not necessarily prefer males based on nest characteristics and may, instead, rely on multiple cues when choosing mates, the relative importance of which should vary depending on context.

Effect of parasite-induced behavioral alterations on juvenile development

Tue, 15 Sep 2009 01:11:11 PDT

Like many trophically transmitted parasites, the trematode Microphallus papillorobustus alters the behavior of its intermediate host, the crustacean gammarid Gammarus insensibilis, in a way that favors its vulnerability to definitive hosts (aquatic birds). Parasitized females still produce eggs, but because juvenile development occurs inside the female marsupial brood pouch, young gammarids are subject to the same risk of predation as their mothers until they exit the marsupium. We explored the idea that developing juveniles can adjust their developmental schedule in a state-dependent manner according to the parasitic status of the mother. We predicted that juveniles from parasitized females would accelerate their development, or exit the marsupium at an earlier stage, to avoid predation by birds. Contrary to our expectations, we observed the opposite, that is, juveniles from parasitized females exited the marsupial brood pouch significantly later than those from uninfected mothers. We discuss these results in relation to current ideas on host manipulation by parasites in ecosystems.

Breeding systems, climate, and the evolution of migration in shorebirds

Garcia-Pena, G. E., Thomas, G. H., Reynolds, J. D., Szekely, T. — Tue, 15 Sep 2009 01:11:11 PDT

Migratory behavior incurs energetic costs that may influence the time and energy available for reproduction including territory establishment, courtship, pair formation, incubation, and brood care. Conversely pair formation and parental care may leave less time and energy available for migration and other nonbreeding behaviors. Therefore, natural selection favoring migratory behavior may influence breeding system evolution and vice versa. We used phylogenetic comparative methods to investigate relationships between migration distance and the wide diversity of breeding systems in shorebirds (sandpipers, plovers and allies). Consistent with previous studies, we show that long-distance migration is associated with reduced male care across shorebird species. We then use directional phylogenetic analyses to test whether migration distances have tended to increase or decrease over time and whether such evolutionary changes have preceded or followed changes in parental care. We show that evolutionary transitions from short-distance migration to long-distance migration have coevolved with changes from full biparental care to reduced male care. Furthermore, our directional analyses suggest that increments in migration distance are more likely to have preceded reductions in male care than vice versa. We also show that male polygamy is associated with northern breeding latitudes when the nonbreeding latitude is controlled statistically. Although this suggests that mating systems, parental care, and migration have more complex relationships than previously thought, our results are consistent with the hypothesis that migration influences breeding system evolution.

Male songbirds provide indirect parental care by guarding females during incubation

Fedy, B. C., Martin, T. E. — Tue, 15 Sep 2009 01:11:11 PDT

Across many taxa, guarding of fertile mates is a widespread tactic that enhances paternity assurance. However, guarding of mates can also occur during the nonfertile period, and the fitness benefits of this behavior are unclear. Male songbirds, for example, sometimes guard nonfertile females during foraging recesses from incubation. We hypothesized that guarding postreproductive mates may have important, but unrecognized, benefits by enhancing female foraging efficiency, thereby increasing time spent incubating eggs. We tested the hypothesis in 2 songbird species by examining female behavior during natural and experimentally induced absences of males. Male absence caused increased vigilance in foraging females that decreased their efficiency and resulted in less time spent incubating eggs. Male guarding of nonfertile females can thus provide a previously unrecognized form of indirect parental care.

Ecological, social, and reproductive factors shape producer-scrounger dynamics in baboons

King, A. J., Isaac, N. J.B., Cowlishaw, G. — Tue, 15 Sep 2009 01:11:12 PDT

Producer–scrounger models are used to explain the tactics of socially foraging animals where individuals can either search for their food (produce) or join the food discoveries of others (scrounge). However, the empirical testing of such models has generally been restricted to indoor aviary experiments. Here, we examine the social foraging tactics of naturally foraging wild chacma baboons (Papio ursinus). Thirty-six adult baboons from 2 groups were observed during full-day follows: Data from nearly 10 000 foraging events were analyzed using cross-classified, generalized linear mixed models. First, as predicted by producer–scrounger models, we show that baboons altered their foraging tactics in accordance with food patch size and spatial position in the group. Second, we show that the relative characteristics of cofeeding individuals were crucial: In particular, among females, individuals were more likely to scrounge from foraging neighbors who were subordinate and with whom they had a strong social affiliation. However, we found no effect of kinship. Finally, we found that female reproductive state influenced female foraging tactics (females scrounged more from male neighbors when pregnant and less when fertile), but the reproductive state of female neighbors had no such effects on male foraging tactics. These results suggest that, in addition to broad-scale ecological and group-level influences, a myriad of social and reproductive factors can shape producer–scrounger dynamics for wild animals living in complex social groups.

Behavioral adaptation of Pallas's squirrels to germination schedule and tannins in acorns

Xiao, Z., Gao, X., Jiang, M., Zhang, Z. — Tue, 15 Sep 2009 01:11:12 PDT

Using acorns from Castanea henryi (CH) and Quercus variabilis (QV) with contrasting germination schedule (related to food perishability) and tannin levels, we conducted field experiments in a subtropical forest in Southwest China to investigate how free-ranging Pallas's squirrels (Callosciurus erythraeus) utilize acorns as long-term storage based on the food perishability and high-tannin hypotheses. Though QV acorns germinated much earlier than CH ones, we found that Pallas's squirrels hoarded more high-tannin QV acorns over low-tannin CH ones, supporting the high-tannin hypothesis (but not the food perishability hypothesis). However, several other predictions derived from the food perishability hypothesis received sound support: nondormant QV acorns had their embryos removed with a higher probability (68.5%) than dormant CH ones (8.8%) and embryo-removed acorns had a much lower germination success but had a higher probability surviving as long-term storage. During the caching-recovery process, hoarding animals actively detected acorn state (dormant or not) and removed acorn embryos with an increasing probability in subsequent hoarding events. In addition, embryo-removed acorns could serve as long-term storage because they had a very low probability being infested by fungi as intact acorns did during the time of storage. We conclude that tree squirrels can differentially respond to acorn germination and remove the embryos of nondormant acorns more frequently as long-term storage, but tannin level is more important in determining whether a given acorn is hoarded or not. Combined with the studies from North America, our results suggest convergent evolution of acorn hoarding behavior in tree squirrels across different continents.

Inbreeding avoidance through cryptic female choice in the cannibalistic orb-web spider Argiope lobata

Welke, K., Schneider, J. M. — Tue, 15 Sep 2009 01:11:12 PDT

The adaptive value of polyandry in the absence of direct benefits is often assumed to lie in the production of more viable or more attractive offspring, mediated by additive genetic effects. Alternative models propose nonadditive effects through the selective matching of compatible genomes. If genetic incompatibility, for example, through hybridization, inbreeding, or selfish genetic elements, reduces viability of offspring, selection should favor pre- or postcopulatory mechanisms of inbreeding avoidance. Postcopulatory inbreeding avoidance might be achieved by polyandry in combination with cryptic female choice. Because female spiders have paired and independent sperm storage organs that are only filled one at a time, they have been suggested to be ideal organisms to investigate cryptic female choice. Here we used orb-web spiders of the Mediterranean species Argiope lobata to investigate whether females treat ejaculates from siblings or nonsiblings differently. In double-mating trials using sibling and nonsibling males in all possible combinations, we experimentally manipulated which male mated into which sperm storage organ and subsequently counted spermatozoa in these storage organs. This experimental design allowed us to unambiguously assign ejaculates to individual males. We found no differential storage of sperm from first males but a significantly reduced amount of stored sperm from the second male if he was a sibling. Our results suggest that females cryptically chose sperm to trade up to more compatible males through storing different quantities.

Female-specific ornamentation predicts offspring quality in the striped plateau lizard, Sceloporus virgatus

Weiss, S. L., Kennedy, E. A., Bernhard, J. A. — Tue, 15 Sep 2009 01:11:12 PDT

When females vary in reproductive quality, they may be selected to honestly signal that quality and males may be selected to express mate choice based on this variation. In the striped plateau lizard, females with larger and more saturated orange throat patches are of higher phenotypic quality, and males preferentially associate with brighter females. Here, we assess whether this female ornament conveys fitness benefits by relating female ornamentation to offspring quality. We housed groups of male and female Sceloporus virgatus in outdoor enclosures, tracked the seasonal color development of females to determine peak ornament expression, measured offspring body condition from hatching to day 180, and measured offspring sprint speed at day 180. Although we did not eliminate the possibility of assortative mating within enclosures, we controlled for these potential effects by exposing females to small groups of similarly sized males and by including maternal body size, maternal body condition, and egg mass as covariates in our statistical models. Offspring body condition was reliably predicted by female ornament size but not by ornament color intensity or saturation. Similarly, offspring sprint speed was predicted only by ornament size and not by color intensity or saturation. Females with large ornaments tended to produce offspring with higher body condition and faster offspring than did females with small ornaments. These results are consistent with the hypothesis that males may gain fitness benefits from preferentially allocating their reproductive effort toward females with larger orange patches by producing higher quality offspring. Possible mechanisms underlying such female-ornament–offspring-quality relationships are discussed.

Female ornamentation and directional male mate preference in the rock sparrow

Griggio, M., Devigili, A., Hoi, H., Pilastro, A. — Tue, 15 Sep 2009 01:11:12 PDT

Albeit there is growing evidence that males prefer to mate with ornamented females, it has been suggested that the production of costly ornaments may reduce female fecundity, hence favoring males with a preference for females with average ornamentation. In the rock sparrow, Petronia petronia, males and females possess a sexually selected patch of yellow feathers on the breast (a carotenoid-based trait). To test whether males prefer females with the largest ornament or average ornamented females, male rock sparrows were simultaneously faced with 3 conspecific females differing in breast patch size and a female house sparrow as a control. We found that the house sparrow and rock sparrow female with the smallest patch were least preferred, and males showed a clear proximity preference for the females with the above average–sized patch. Our results demonstrate that, contrary to theoretical predictions, a directional preference for female ornament was observed. Directional male preference may arise as consequence of a male's sensory bias or may be associated with indirect (genetic) benefits of choosing ornamented females, if ornament size is correlated with female genetic quality. Clearly, more work is necessary to identify the conditions under which directional preference for female ornament arises.

Sexual selection on body size and secondary sexual characters in 2 closely related, sympatric chameleons in Madagascar

Karsten, K. B., Andriamandimbiarisoa, L. N., Fox, S. F., Raxworthy, C. J. — Tue, 15 Sep 2009 01:11:12 PDT

In polygynous mating systems, sexual selection can drive the evolution of male characters beneficial to winning fights for mates (intrasexual selection), for improving the mating success of males through mate choice (intersexual selection), or both. However, it may be difficult to disentangle the relative contributions of intra and intersexual selection on multiple traits that may be of dual utility. We used field arena trials to determine which morphological traits best explained male fighting ability and male mating success in 2 species of chameleons in Madagascar, Furcifer labordi and Furcifer verrucosus. In F. labordi, male fighting success was best predicted by body size and size-corrected shorter rostral appendages and male mating success was best predicted by width of the rostral appendage and body size. In F. verrucosus, we found strong intrasexual selection for increased male body size and fewer counted dorsal cones, a trait that may correspond to increased age and experience. Although females in this species are generally passive toward courting males, male mating success with potentially receptive females is highly variable. Fewer counted dorsal cones and larger size-corrected casque height best explained male mating success; traits that may be selected by the female and/or correlated with increased age and experience. Although difficult to determine the relative contributions of intra and intersexual selection on traits with dual benefits (both fighting and mate choice), we documented both types of selection on body size and secondary sexual characters in these 2 chameleon species.

Birdsong tuned to the environment: green hylia song varies with elevation, tree cover, and noise

Tue, 15 Sep 2009 01:11:12 PDT

Animals that communicate acoustically must compete for acoustic space in order to convey their signals effectively. Tropical rainforest birds live in an extremely diverse acoustic community consisting of other birds, mammals, frogs, and many insects. Insects are notable for often producing continuous bands of sound energy at constant frequencies, which vary between species and across habitats. We examined how green hylia (Hylia prasina) song frequencies correlate to insect-generated spectral profiles of ambient noise. We also examined how the environment influenced song frequency by using remote sensing to quantify environmental variables. Using path analysis, we assessed the relative effects of elevation, tree cover, precipitation, and insect sounds on green hylia song frequency. Environmental variables were found to directly influence green hylia song frequencies. Specifically, green hylia sang at lower frequencies at higher elevations and under reduced canopy cover. The environment also influenced green hylia song indirectly through its effect on insect sounds. Green hylia sang at lower frequencies presumably to avoid masking by lower frequency insect sounds. Habitat-dependent divergence in songs within species potentially plays an important role in ecological speciation through its impact on species recognition and mate choice. Our data show that factors related to climate, vegetation, and vocal community can promote such habitat-dependent song variation.

Why some memories do not last a lifetime: dynamic long-term retrieval in changing environments

Dunlap, A. S., McLinn, C. M., MacCormick, H. A., Scott, M. E., Kerr, B. — Tue, 15 Sep 2009 01:11:12 PDT

Memory is a fundamental component of learning, a process by which individuals alter their behavior through experience. Although memory most likely has explicit costs such as synaptic maintenance and metabolic demands, there are also implicit costs to memory, in particular, the use of information that is no longer appropriate or is incorrect. Specifically, the period of retrievability for memories, or "memory window," should be sensitive to the rate of environmental change of information stored in memory. Much empirical data suggest that memory length—this period of retrievability—changes with both the age and state of the individual. Here, we use a dynamic programming approach to examine how optimal memory retrieval might change within the lifetime of the individual learner. We find that optimal memory length varies with both age and state (e.g., energy reserves) of the organism and that features of the environment determine how this change in memory occurs. In our model, retrieval decreases as the environment becomes unreliable but roughly increases with the cost of living. Cost of living interacts with the state of the organism: with high cost of living, an organism in a very poor state should have a long memory length, but an organism in a very good state with low costs of living should have a short memory length. Finally, we find there are circumstances where it is optimal for memory retrieval to decline toward the end of the lifetime. Because this framework does not incorporate inevitable degradation of neural mechanisms, this result implies that memory loss with age might actually be adaptive.

Worker reproduction in mixed-species colonies of honey bees

Tue, 15 Sep 2009 01:11:12 PDT

To explore reasons for the unusually high rates of worker ovary activation in Apis cerana, we investigated the reproductive physiology of workers in conspecific and mixed-species colonies of A. cerana and its sibling species Apis mellifera under queenright and queenless conditions. In both queenless and queenright conspecific colonies, the proportion of A. cerana workers with activated ovaries was significantly greater than the proportion of A. mellifera workers with activated ovaries. Apis cerana workers showed significantly greater ovary activation in queenright mixed-species colonies than in conspecific queenright colonies. Moreover, there was significantly greater ovary activation in A. cerana workers in mixed-species colonies headed by A. mellifera queens than A. mellifera workers in mixed-species colonies headed by A. cerana queens. Apis mellifera workers in conspecific queenless colonies showed significantly greater ovary activation than those in mixed-species queenless colonies. Quantification of the chemical components of mandibular gland pheromones of queens of the 2 species showed that they are similar. Combined, our results show that queen signals have been preserved between the 2 species and that workers respond to the heterospecific signals from queens. However, despite the similarity in the queen mandibular gland fatty acid secretions between the 2 species, workers respond differentially toward hetero- and conspecific queens.

Peripheral obstructions influence marmot vigilance: integrating observational and experimental results

Bednekoff, P. A., Blumstein, D. T. — Tue, 15 Sep 2009 01:11:12 PDT

Animals generally allocate some time during foraging to detecting predators. We used a combination of observations and an experiment to examine how vegetation height and peripheral obstructions influence vigilance by foraging yellow-bellied marmots (Marmota flaviventris). First, we analyzed a large sample of observations of marmots foraging in nature. Marmots increased vigilance with vegetation height and reared on their hind legs when in tall vegetation. Second, we observed that marmots foraged in locations with lower vegetation than randomly selected sites in the same meadow. These observations suggest that marmots account for what they can see while foraging but do not rule out the influence of other factors correlated with vegetation height. Therefore, we experimentally blocked the view for 3 sides for marmots feeding on a controlled food source. When the apparatus blocked their vigilance, marmots were less vigilant when foraging, often moved outside the apparatus, and showed heightened vigilance while outside the apparatus. Peripheral obstructions explained more of the variance in our experimental than in our observational results. Together, our results demonstrate that marmots employ antipredator behavior to compensate for peripheral obstructions. Long-term studies show that marmots go locally extinct more often in areas with more obstructions to vigilance. Thus, marmots likely face greater predation risk in those areas, despite the behavioral responses documented in this study.

Male dominance influences pheromone expression, ejaculate quality, and fertilization success in the Australian field cricket, Teleogryllus oceanicus

Thomas, M. L., Simmons, L. W. — Tue, 15 Sep 2009 01:11:12 PDT

The outcome of fights between males can often represent an honest signal of male quality and are therefore widely used by females in mate choice. Indeed, female preference for males that win fights has been demonstrated in numerous animal taxa, and many recent studies have focused attention on how subordinate males compensate for this disadvantage through postcopulatory mating strategies, such as increased investment in their ejaculates. Here, using the Australian field cricket, Teleogryllus oceanicus, we show that rather than investing more in postcopulatory strategies, subordinate males invest in an alternative precopulatory mating approach. We find that subordinate males produce ejaculates of lower quality than dominate males and sire less offspring when competing for fertilizations. However, subordinate males upregulate the quantity of a number of cuticular compounds that have previously been shown to increase male mating success. Our results suggest that male reproductive success is likely to result from the interaction of multiple traits in this species.

Mate-guarding behavior in clam shrimp: a field approach

Benvenuto, C., Knott, B., Weeks, S. C. — Tue, 15 Sep 2009 01:11:12 PDT

Precopulatory mate guarding is a complex behavior, influenced by many social and physiological factors, representing a case of intersexual conflict. Mate guarding has often been analyzed with the aid of theoretical models. In these models, it is commonly predicted that mate-guarding time is influenced by encounter rates between males and females, the contenders’ relative sizes, and the possible interaction among males (i.e., "takeovers": one guarding male displacing another). The factors influencing male and female guarding decisions have been measured in laboratory experiments but never under natural field conditions. In this field-based study, we observed mate-guarding couples of the clam shrimp Limnadia badia in ephemeral pools on granite rock outcrops in Western Australia. We recorded guarding duration, focusing on the factors considered important in mate-guarding models: male and female size, population density, sex ratio, operational sex ratio, and the status of female receptivity. We also estimated time budgets for males, the possibility of male takeovers, and the potential role of female resistance. We found that female receptivity stage (how close the female was to molting), small male size, and low absolute female presence are key factors in decreasing mate-guarding duration. This study adds a field dimension to manipulative laboratory projects and theoretical models of mate guarding. We were able to observe the simultaneous interactions of multiple factors in the field and to make a robust examination of the ideas of intersexual conflict during mate guarding in these crustaceans.

Trade-offs between markers of absolute and relative quality in human facial preferences

Saxton, T. K., Little, A. C., Rowland, H. M., Gao, T., Roberts, S. C. — Tue, 15 Sep 2009 01:11:12 PDT

Individuals are attuned to cues of quality in potential mates. Mate quality is assessed on both an absolute scale, independent of the observer, and also on a relative scale, dependent on attributes of the observer. Much research has focused on how individuals respond to either absolute or relative quality in mate choice, but how these dimensions are weighted during mate-choice decisions is poorly understood and has recently attracted much theoretical interest. Here, we examine the interplay between women's facial preferences for a measure of absolute quality (sexual dimorphism) and one of relative quality (self-similarity). Women rated the attractiveness of male faces that had been simultaneously manipulated along the dimensions of masculinity and self-similarity in short-term and long-term relationship contexts. Sexual dimorphism had a greater positive effect on ratings than self-similarity, and masculinity and self-similarity had positive combinative effects on ratings of attractiveness. Women's coexpressed preferences for masculine faces combined with their lesser preference for subtly self-similar faces may reflect selection of good genes, promote optimal outbreeding, and give rise to directional selection, even in the presence of a general self-similarity preference.

The cost of virulence: an experimental study of egg eviction by brood parasitic chicks

Grim, T., Rutila, J., Cassey, P., Hauber, M. E. — Tue, 15 Sep 2009 01:11:12 PDT

Hatchlings of some virulent brood parasitic birds have evolved to eliminate host offspring. We experimentally studied the dynamics and potential costs of the egg eviction behavior of hatchlings of the common cuckoo Cuculus canorus in broods of common redstarts Phoenicurus phoenicurus, a cavity nesting host. Eliminating the labor of egg tossing per se improved the cuckoo chick's growth during the eviction period by ~20–30%. Evictor cuckoo chicks recovered from the cost of egg tossing to fledge at similar masses compared with solitary chicks, although they did so at older ages. Foster parents fed evictor chicks less often compared with nonevictors. Feeding frequencies by hosts to evictors correlated negatively with eviction effort as evicting chicks often appeared to ignore fosterers offering food. Nest cup steepness was negatively related to eviction success and positively to age at first eviction. We propose that eviction behavior by cuckoo hatchlings is favored by selection because the costs of eviction are much lower than the costs of cohabitation with host chicks.

Males use sex pheromone assessment to tailor ejaculates to risk of sperm competition in a butterfly

Larsdotter Mellstrom, H., Wiklund, C. — Tue, 15 Sep 2009 01:11:12 PDT

In polyandrous butterflies males transfer a large, nutritious ejaculate at mating. Larger ejaculates delay female remating and confer an advantage in sperm competition. However, large ejaculates are costly, potentially selecting for male adjustment of ejaculate size to the risk of sperm competition. Here, we test if male ejaculate size in the butterfly Pieris napi varies with male density, and whether males assess sperm competition risk using the male sex pheromone citral as a cue. The results conformed to sperm competition theory and showed that male P. napi tailored their reproductive investment in response to the risk of sperm competition; ejaculates transferred by males in the high male density treatments were on average 23% larger than ejaculates transferred at low male densities. The results also show for the first time that the sex pheromone citral was used by males to assess male density; ejaculates transferred by males in presence of added male sex pheromone were 19% larger than ejaculates transferred in the control. In conclusion, the study shows how the sex pheromone not only facilitates female acceptance when dispensed by courting males but also allows males to assess the degree of male competition for matings.

Protein content of diets dictates the daily energy intake of a free-ranging primate

Tue, 14 Jul 2009 00:07:55 PDT

An important goal in nutritional ecology is to understand what governs the diet selection of free-living animals. Relevant information is however scarce because of the considerable challenges of collecting and interpreting such data. Here we use recent advances in nutritional theory to analyze data on food selection and nutrient intake by wild spider monkeys (Ateles chamek). We show that hypotheses traditionally used to explain vertebrate diet selection, such as energy or protein maximization, or avoidance of plant secondary metabolites, cannot explain the observed pattern of nutrient intake. Instead, spider monkeys maintained a stable daily protein intake but allowed total energy intake to vary as a function of the composition of available food items. A similar "protein-leverage effect" has been reported in humans for whom it appears to play a role in the development of obesity.

Parasitic cowbirds may defeat host defense by causing rejecters to misimprint on cowbird eggs

Strausberger, B. M., Rothstein, S. I. — Tue, 14 Jul 2009 00:07:55 PDT

Experiments suggest that some hosts that reject parasitic brown-headed cowbird (Molothrus ater) eggs develop egg recognition by imprinting on their own eggs, probably at the first nest naïve birds attend. This raises the possibility that parasitism of naïve individuals might cause them to mistakenly misimprint on, and accept, cowbird eggs. In an egg-learning experiment designed to cause misimprinting, hosts accepted cowbird eggs when they had laid only 1 egg even though most rejected cowbird eggs when nests had ≥2 host eggs. These findings show that cowbirds can cause misimprinting by parasitizing naïve hosts. If done opportunistically, misimprinting should become more likely as cowbird abundance increases. In accord with this expectation, simulated brood parasitism showed that 3 host species that usually reject cowbird eggs were more tolerant of cowbird eggs in the Great Plains, where cowbirds reach maximal historic abundance, than in eastern North America where cowbirds are less common. This relation between parasite abundance and host responses is opposite to that found in cuckoo hosts. In addition, these 3 rejecter species had high rates (10.8–30.4%) of natural cowbird parasitism at an Illinois site where cowbirds are extremely, and historically, abundant. These rejecters accepted most cases of researcher-detected parasitism, even though they rarely accept where cowbirds are less common. Despite the potentially high cost resulting from egg rejection, we demonstrate that parasitism of "rejecters" can be adaptive for cowbirds particularly when host egg recognition involves learning.

Nutritional enrichment increases courtship intensity and improves mating success in male spiders

Lomborg, J. P., Toft, S. — Tue, 14 Jul 2009 00:07:55 PDT

The development of male sexual ornaments and the intensity of male courtship behavior are often used by females as criteria for mate choice and by other males to evaluate the strength of a rival. We tested the hypotheses that courtship intensity and mating success depend on the males' nutritional status (enriched or deficient) and that courtship intensity predicts mating success in males of the same nutritional status. We used wolf spiders, Pardosa prativaga, which have an elaborate display of courtship behaviors, including encircling, palp vibrations, abdomen vibrations, hopping, etc. Viability parameters indicated enhanced condition of enriched males. Mating success was higher for nutrient-enriched males in direct competition with deficient males. Enriched males had higher courtship intensity and were also larger (carapace width) but not heavier than deficient males. The statistical analysis indicated that diet effects on courtship intensity were indirect, through its effect on size. In competition tests between males of equal mass and the same diet treatment, the previously most active male (high levels of palp vibrating, abdomen vibrating, and hopping) had the highest mating success, though this result depended on male nutrient status. The widely used residual condition index (RCI) did not distinguish the treatments. It is suggested that the index is unsuitable in a situation of nutritional stress caused by nutrient imbalance. The results underscore the importance of nutrient balancing to all aspects of performance also in predatory animals.

Vigilance and predation of a forest-living bird species depend on large-scale habitat structure

Griesser, M., Nystrand, M. — Tue, 14 Jul 2009 00:07:55 PDT

Prey often use visual cues to detect predators, and consequently, many studies have assessed the effect of small-scale habitat structure on prey antipredator vigilance. This scale may be inappropriate to assess the link between habitat structure and vigilance, however, because visually hunting predators often detect prey from several hundred meters away. As a result, large-scale habitat structure could affect both the hunting decisions of predators and antipredator behaviors of prey. Here we investigated the effect of small- and large-scale habitat structure, as well as group composition (kinship) on vigilance allocation of breeders in the Siberian jay Perisoreus infaustus. Vigilance had an antipredator function and was increased after exposure to a predator model. Small-scale habitat structure did not affect vigilance rates, however, habitat structure of the whole territory, measured as the proportion of visual cover, affected vigilance depending on group composition. Breeders with retained offspring (kin) in their group were more vigilant in managed open territories than on pristine dense territories, whereas breeders without kin in their groups did not adjust vigilance rates in relation to large-scaled habitat structure. Earlier studies have revealed that hawks, the main predators of jays, primarily kill non-kin group members living in groups inhabiting open territories. Therefore, we suggest that breeders adjusted their vigilance depending on the habitat-specific predation risk to protect their retained offspring. This demonstrates that large-scale habitat structure affects predator–prey interactions and is crucial to understanding spatial variation in antipredator allocation and mortality.

Beyond waist-hip ratio: experimental multivariate evidence that average women's torsos are most attractive

Donohoe, M. L., von Hippel, W., Brooks, R. C. — Tue, 14 Jul 2009 00:07:55 PDT

One of the most iconic findings in human behavioral ecology is the fact that women with waist-hip ratios (WHRs) of approximately 0.7 are most attractive and that this ratio indicates maximum fecundity and reproductive value. However, the effects of WHR and of other indices of body shape and size on attractiveness are far from fully resolved. We adopt a recently developed method that combines multivariate manipulation of experimental stimuli with evolutionary selection analysis to test the linear and nonlinear effects of waist, hip, and shoulder width and the interactions between these traits on the attractiveness of 200 line-drawn models to 100 men. There was no general support that WHR or body mass (expressed as perimeter–area ratio) significantly influences attractiveness. There was, however, strong preference for average values of all 3 traits indicating that attractiveness is due to the tight integration of these 3 traits. We plot the mean waist and hip sizes of 8 samples of women on our response surface, including Playboy centerfolds, models from the 1920s and 1990s, Australian escorts, and Australian women in 4 different age categories (collectively we refer to this latter group as the "regular women"). The regular women in the 25- to 44-year age-group were closest to the peak attractiveness value on our response surface. Our results highlight the strong integration of and interrelationships among different parts of the body as determinants of attractiveness.

Preexisting behavior renders a mutation adaptive: flexibility in male phonotaxis behavior and the loss of singing ability in the field cricket Teleogryllus oceanicus

Tinghitella, R. M., Wang, J. M., Zuk, M. — Tue, 14 Jul 2009 00:07:55 PDT

Flexibility in behavior and other traits can pave the way for rapid evolutionary change. A wing mutation, "flatwing," eliminates the ability of >90% of male field crickets (Teleogryllus oceanicus) from one Hawaiian population to produce song to attract females. The morphological change was favored because calling is risky in Hawaii, attracting deadly parasitoid flies. An earlier study suggested that instead of calling, silent flatwing males use satellite behavior, approaching one of the few remaining callers and intercepting females attracted to them. Satellite-like behavior may have existed as a behavioral option prior to the wing mutation, accommodating the loss of singing ability, or behavior may have changed simultaneously with the spread of the mutation. In phonotaxis trials, males from different populations across the crickets’ range varied in the distance at which they settled from the source of broadcast song, behaving more or less like satellites. Anecdotally, we noted satellite behavior in all populations, and importantly, males from the mutated population and its direct ancestor behaved similarly. This suggests that the alternative behavior is not strictly associated with the mutation and instead predated the change in morphology. We hypothesized further that satellite behavior may have been preexisting because it is beneficial under other circumstances, such as poor mating success. Virgin males did not show enhanced phonotaxis relative to multiply mated males, however. We conclude that satellite behavior predated the mutation in wing morphology, providing obligately silent males with an alternative method of locating mates and effectively rendering the wing mutation adaptive. Whereas mating history does not appear to influence phonotaxis behavior in males, other factors such as the acoustic environment and demographic conditions may be important contributors to behavioral decisions during male mate location.

Maternal weight, offspring competitive ability, and the evolution of communal breeding

Tue, 14 Jul 2009 00:07:55 PDT

Despite the widespread occurrence of communal breeding in animal societies, the fitness consequences for mothers are poorly understood. One factor that may have an important influence on the net benefits mothers gain from breeding communally is the competitive ability of their offspring, as mothers are likely to gain substantial advantages from producing young who can outcompete the offspring of other females for access to resources. Here, we investigate the factors that influence offspring competition in the communally breeding banded mongoose (Mungos mungo). We show that heavy offspring are more likely to win competitive interactions with their littermates. Heavy offspring also receive more care and are more likely to survive to independence in large communal litters where competition is most intense. Our results also indicate that offspring weight at emergence is positively correlated with the weight of the mother at conception. As a consequence, the offspring of heavy mothers are likely to enjoy marked competitive advantages during early life. Together, our findings strongly suggest that the competitive ability of offspring will influence the costs and benefits that females experience while breeding communally and highlights the need for closer examination of the factors that influence offspring competitive ability and the influence this may have on the evolution of communal breeding.

Reproductive effort in biparental care: an experimental study in long-lived Cape gannets

Bijleveld, A. I., Mullers, R. H.E. — Tue, 14 Jul 2009 00:07:55 PDT

Life-history theory predicts a trade-off between current and future reproduction, such that long-lived species should not increase their reproductive effort (RE) at a cost to their own survival. In species with long-term pair bonds and biparental care, each parent must balance its reproductive investment against that of its partner. Although the effects of "handicapping" studies on the focal individual are sometimes difficult to interpret, they are a powerful approach for investigating compensatory responses of the partner. In the present experiment, we manipulated flying ability of one parent in long-lived Cape gannets (Morus capensis), thereby indirectly increasing the demands on RE of the unmanipulated partner. Handicapped birds doubled their foraging trip duration and reduced nest attendance. Their partners showed behavioral compensation via increased nest attendance for chicks younger than 30 days and increased foraging trip frequency for older chicks. The behavioral responses of partners did not fully compensate for the reduced care of handicapped adults. For manipulated nests, overall foraging trip frequency was 21% lower, chicks were left unattended at 5 days younger, and their growth and survival was reduced compared with control nests. Handicapped adults lost 10% of their body mass during the experiment, but their partners showed no decrease in body mass. Our results show that long-lived Cape gannets can increase current RE when needed, without negative effects on body condition or survival. The reduced care of one parent was partly compensated for by its partner, and remaining costs were borne by the chick.

An avian eavesdropping network: alarm signal reliability and heterospecific response

Magrath, R. D., Pitcher, B. J., Gardner, J. L. — Tue, 14 Jul 2009 00:07:55 PDT

Alarm calls potentially provide information about predators to heterospecifics, but little is known about patterns of eavesdropping among species. Many cases of eavesdropping in birds and mammals involve social species in mixed-species groups, but this is not always true and the reliability of information may also be critical. We used a playback experiment and observations of natural alarm calling to test for understanding of aerial "hawk" alarms among 3 species of passerine and assess call reliability. Superb fairy-wrens and white-browed scrubwrens are ecologically similar and can share mixed-species flocks, whereas New Holland honeyeaters are ecologically distinct and do not flock with the other species. Fairy-wrens and scrubwrens fled to cover to each other's alarm calls, but they also both fled to honeyeater alarms. Honeyeaters fled to scrubwren but usually not fairy-wren alarms. The pattern of heterospecific responses appears related to call reliability from each species’ perspective. Honeyeaters called only to predators of all 3 species and so provided reliable information to all. From a honeyeater's perspective, fairy-wrens were least reliable, as they gave 52% of their calls to nonpredators, whereas scrubwrens gave only 18% to nonpredators. However, from a scrubwren's perspective, fairy-wrens were largely reliable because most calls to nonpredators were to red wattlebirds, which pose a physical threat to fairy-wrens and scrubwrens but not honeyeaters. We conclude that there can be mutual responses to alarm calls between ecologically distinct species, that responses can be symmetrical or asymmetrical between species, and that call reliability appears to affect response.

Secondary sexual trait size reveals competitive fertilization success in Drosophila bipectinata Duda

Polak, M., Simmons, L. W. — Tue, 14 Jul 2009 00:07:55 PDT

The evolution of male secondary sexual traits traditionally has been ascribed to precopulatory sexual selection. In contrast, the importance of postcopulatory sexual selection for the evolution of secondary sexual traits is uncertain, and what little evidence exists for this process to contribute to the evolution of such traits is mixed. Here we test the hypothesis in Drosophila bipectinata Duda that the male sex comb, a rapidly evolving secondary sexual trait, is under positive postcopulatory sexual selection. We extracted replicate genetic lines exhibiting relatively large and small sex comb size from a natural population. Males from these lines were subjected to an assay of competitive fertilization ability, measured as P₂, the proportion of a female's clutch of eggs fertilized by the second male to mate. Males with the largest sex combs sired more offspring than less ornamented individuals, demonstrating for the first time in any Drosophila species that postcopulatory sexual selection favors increasing sex comb size. This study identifies a postcopulatory selective mechanism that may be contributing to the evolutionary diversification of a secondary sexual trait.

Brood size in a polyembryonic parasitoid wasp is affected by relatedness among competing larvae

Segoli, M., Harari, A. R., Bouskila, A., Keasar, T. — Tue, 14 Jul 2009 00:07:55 PDT

Brood size has important implications for the fitness of both parents and offspring. In polyembryonic parasitoid wasps, each egg develops into many genetically identical embryos through clonal division inside the host. Thus, offspring may have the potential to affect brood size by adjusting the degree of embryonic division. In some species, a proportion of embryos develop into soldier larvae, which attack competitors inside the host. This may be another mechanism for offspring to affect final brood size. We investigated the effect of relatedness between competing clones on brood size in the polyembryonic wasp Copidosoma koehleri. We predicted that final brood size would be affected by the number and relatedness between competing clones inside the host. Additionally, we predicted that due to a competitive asymmetry between male and female clones (apparently only female clones produce a soldier larva), this effect would depend on the sex composition of wasps inside the host. We allowed 2 wasp eggs (laid either by 1 female or by different females) to develop in a host and counted the emerging adults. Relatedness between male clones did not affect brood size. However, female-containing broods of related clones were larger than broods of nonrelated clones, suggesting higher aggression of the soldier toward less related individuals. Dissections of hosts parasitized by 2 clones indicate that normally only 1 soldier survives and that it often eliminates unrelated clones. Thus, offspring control over brood size in response to relatedness is probably mediated by soldier aggression and not by clonal division.

Female reproductive tactics in a sex-role reversed pipefish: scanning for male quality and number

Silva, K., Almada, V.C., Vieira, M.N., Monteiro, N.M. — Tue, 14 Jul 2009 00:07:55 PDT

Theoretical studies predict that females should invest in current reproduction according to both the expected payoffs from mating with different-quality males and their future mating prospects. The Syngnathidae family, with its male pregnancy together with the occurrence of varying degrees of sex-role reversal, constitutes an exceptional model to study female allocation strategies. The present work tests for the influence of male availability and quality (translated into body size) on the egg allocation pattern of different-sized females of the sex role–reversed pipefish Syngnathus abaster. Besides revealing a multiple mating strategy and showing that females do not produce enough eggs to fully occupy a male's brood pouch during the extent of a pregnancy, results reveal a complex pattern with different-sized females adopting different investment tactics. In contrast to small, less attractive females, who show a much more constant reproductive effort through the tested mating contexts, large females seem able to monitor the number and quality of available males responding accordingly by 1) laying more eggs in the presence of several large males or saving efforts for future breeding and 2) laying larger eggs in larger males while depositing smaller ones in lower quality individuals as a consequence of a serial mating process (large males first, small males later).

Cues, concessions, and inheritance: dominance hierarchies in the paper wasp Polistes dominulus

Zanette, L., Field, J. — Tue, 14 Jul 2009 00:07:55 PDT

Hierarchies constitute the base of many social groups. Hence, understanding how they are established is critical. Here we examine how hierarchies are formed in foundresses associations of the common paper wasp Polistes dominulus. By comparing field data with computer simulations, we evaluate order of arrival at the nest, body size, facial color patterns, and within-group kinship structure as determinants of inheritance rank. Hierarchies (ranks 1–5) were experimentally inferred for 53 nests. Overall, the order in which foundresses arrived at the nest and their body size were not significantly correlated with rank. A foundress's rank was negatively correlated with the number of full sisters it had in its group. Highly ranked wasps (ranks 1 and 2) were less likely to share a nest with their full sisters than wasps of lower rank. A wasp's rank was not determined by the relative rank of its nest-mate sisters. A foundress's rank was significantly correlated with the size of its black clypeal marks, but the number of foundresses with clypeal marks in each nest was small. On 15 of 20 nests where wasps with marks were present, only 1 wasp had such marks. Overall, our results suggest that within-group relatedness structure is important in the establishment of dominance hierarchies in P. dominulus foundress associations.

A behavioral syndrome linking courtship behavior toward males and females predicts reproductive success from a single mating in the hissing cockroach, Gromphadorhina portentosa

Logue, D. M., Mishra, S., McCaffrey, D., Ball, D., Cade, W. H. — Tue, 14 Jul 2009 00:07:55 PDT

Suites of correlated behaviors, or "behavioral syndromes," have been shown to occur throughout the animal kingdom. Behavioral syndromes involving sexual selection are expected to have significant evolutionary ramifications, but few studies have linked behavioral syndromes to sexual selection. We measured the behavior of male hissing cockroaches (Gromphadorhina portentosa) during male–male competition, female choice, and 3 other ecologically relevant contexts and quantified between-context correlations in behavior. We found that aggression directed toward an opponent and retreat and courtship elicited from an opponent were repeatable among males, suggesting that individuals exhibit stable behavioral types in the context of male–male interaction. Our analyses also revealed a "fast–slow" syndrome, linking behavior in a self-righting context to behavior in a foraging context. In contrast to data from several other species, fast–slow scores in hissing cockroaches were not correlated with aggression in a male–male context. Finally, we identified a new type of behavioral syndrome, which we call "libido." Libido was defined by a positive relationship between courtship directed toward opponents in a male–male context and courtship directed toward potential mating partners in a male–female context. Among males that copulated, libido scores predicted reproductive success. We conclude that the libido syndrome, coupled with sexual selection favoring high courtship intensity in a male–female context, may be responsible for the persistence of male–male courtship behavior in this population.

Aggressive Ural owl mothers recruit more offspring

Tue, 14 Jul 2009 00:07:55 PDT

Animals are thought to adjust their behavior optimally to any given environment. So-called behavioral syndromes, or consistent patterns of behavior across environments, contradict this assumption of unlimited plasticity. We studied nest defense aggressiveness of female Ural owls (244 females with 482 breeding attempts) breeding in a highly variable environment created by fluctuations in the abundance of their main prey (field and bank voles) across years. Ural owls were more aggressive when voles were increasing in density as well as when the Ural owls had large brood sizes and laid early in the season. Aggressive nest defense was highly repeatable between breeding attempts (r = 0.52 ± 0.05 standard error), but individuals also differed in their plasticity (the extent to which they adjusted the level of their aggression to the varying food conditions). Fierce nest defenders produced more recruits to the local breeding population, but a female's survival was not affected by her intensity of nest defense. A path analysis revealed that nest defense aggressiveness, rather than its correlates vole abundance, brood size, or laying date, best explained offspring recruitment. Our findings provide an ultimate explanation for the Ural owl's extremely aggressive nest defense.

A possible case of contemporary selection leading to a decrease in sexual plumage dimorphism in a grassland-breeding shorebird

Schroeder, J., Lourenco, P. M., Hooijmeijer, J. C.E.W., Both, C., Piersma, T. — Tue, 14 Jul 2009 00:07:55 PDT

In sexually dimorphic species, males with more exaggerated plumage ornamentation generally have higher body condition, are preferred by females, and have higher reproductive output. In contrast to the majority of studies, we describe that less ornamented males of the monogamous and sexually dimorphic black-tailed godwit Limosa limosa were larger and heavier during late incubation than more ornamented males and were mated with females that laid larger eggs. In females, we detected no such correlations. If paler and larger males indeed have higher fitness, this suggests ongoing selection for a reduction in male ornamentation, leading to a decrease in plumage ornamentation. We found evidence for such a change since 1840: Male ornamentation in museum specimens became progressively less in all our measured plumage traits. One explanation for this could be that formerly sexually selected plumage traits are now selected against and that the sexual plumage dimorphism of West-European breeding black-tailed godwits might be waning. Concomitant with this change in plumage coloration, this species has experienced enormous human-mediated changes in both breeding and nonbreeding habitat, and we suggest that these might have led to increased costs or reduced fitness benefits for highly ornamented male godwits.

Hunting efficiency and predation risk shapes the color-associated foraging traits of a predator

Fan, C.-M., Yang, E.-C., Tso, I-M. — Tue, 14 Jul 2009 00:07:55 PDT

When animals forage or court their behaviors are often constrained by factors such as predation risk. Predator–prey interactions govern the evolution of many behavioral and morphological traits. However, animals with foraging or courtship tightly linked to morphology cannot make quick behavioral adjustments when encountering a dilemma. In this study, we investigate how opposing pressures of maximizing prey intake and minimizing predation risk shape the morphology-associated foraging traits of a sit-and-wait predator. Recently, the conspicuous body colorations of certain orb-weaving spiders have been demonstrated to be attractive to both insect prey and predators. In this study, we performed field manipulations to assess how visual luring signals of such predators trade off opposing pressures of feeding and surviving. We created dummies made of cardboard to test how changing size of conspicuous signal affected attractiveness to prey and predators. Dummies mimicked the coloration pattern and chromatic properties of giant wood spider Nephila pilipes. We found that dummies were similarly attractive to prey and predators as real spiders were. Uniformly yellow colored dummies attracted significantly more prey than those dummies that mimicked the color pattern of N. pilipes. However, such dummies also attracted far more hymenopteran predators. Our findings indicate that current morphology-associated foraging traits of certain animals do not necessarily provide the best feeding performance but reflect a trade-off between opposing pressures of foraging intake and predation risk.

Queenless colonies of the Asian red dwarf honey bee (Apis florea) are infiltrated by workers from other queenless colonies

Tue, 14 Jul 2009 00:07:55 PDT

In all honey bee species studied thus far, 2–4% of the workers were not born in the sampled colony. These unrelated (nonnatal) workers are thought to arise via orientation errors while returning from foraging trips. Interestingly, in colonies of the red dwarf honey bee, Apis florea, the proportion of nonnatal workers increases significantly when the colonies become queenless, and these workers are more likely to have active ovaries and lay eggs than natal workers. As a result, queenless colonies are heavily parasitized with the eggs of nonnatal workers, but the origin of the parasitizing workers is currently unknown. Here we show that workers from queenless A. florea colonies are far more likely to leave their colony and join another colony compared with workers from queenright colonies. Choice experiments showed that these drifted workers are much more likely to join a queenless colony than a colony with a queen. Perhaps surprisingly, not many workers from queenright colonies joined queenless colonies despite the opportunity for direct reproduction in queenless colonies. We suggest that the inclusive fitness benefits of remaining in the natal colony in the presence of the queen exceed the benefits of direct reproduction in an unrelated queenless colony.

Nestling begging increases predation risk, regardless of spectral characteristics or avian mobbing

McDonald, P. G., Wilson, D. R., Evans, C. S. — Tue, 14 Jul 2009 00:07:55 PDT

Models of parent–offspring conflict and nestling begging honesty often assume that signaling is associated with increased predation risk. However, little evidence exists that begging actually increases predation in the context in which it evolved, especially when the potentially modulating effects of parental defense are taken into account. We measured the cost of begging in cooperatively breeding bell miners (Manorina melanophrys) by baiting 168 inactive nests with a wax egg and broadcasting sounds from nearby speakers. Nests were randomly assigned to 1 of 3 treatments: silence, unmanipulated begging calls, or shaped white noise pulses that matched the amplitude envelope of each corresponding begging call. Moreover, half of the nests were placed outside and half inside bell miner colonies, where miners vigorously mob potential nest predators. Predation was not influenced by vegetation cover, distance of the nest from the speaker, or placement inside the colony. Sounds were costly, however, as nests broadcasting begging signals or white noise were predated more often and more quickly than silent controls. Contrary to theoretical predictions regarding "stealthy" design, we found that predators were just as likely to locate nests with broadband white noise playback as nests broadcasting begging signals. Further, there was an interaction between playback amplitude and predator type (avian vs. rodent): Louder playback led to decreased nest survival for those taken by avian predators. As increased begging drives provisioning rates in many species, including bell miners, this reveals an inescapable trade-off between nestling begging intensity, parental provisioning effort, and predation risk.

Personality traits in wild starlings: exploration behavior and environmental sensitivity

Minderman, J., Reid, J. M., Evans, P. G.H., Whittingham, M. J. — Tue, 14 Jul 2009 00:07:55 PDT

Animal personalities, defined as consistent and correlated individual differences in behavioral traits, are suggested to be common in the animal kingdom and can have important fitness consequences. Individual differences in sensitivity to environmental cues are predicted to be part of animal personalities and are important because they will affect an individual's ability to respond to environmental change. Such environmental sensitivity as a personality trait needs further study because existing studies have rarely directly related environmental sensitivity to well-established personality traits such as exploration behavior and have focused on captive animals of specific model species. Using standardized assays of exploration behavior, we show that individual variation in 1) the speed of exploration behavior and 2) the parts of the environment that are explored are repeatable in juvenile wild starlings (Sturnus vulgaris). Environmental sensitivity was measured in separate assays and was not correlated with the speed of exploration behavior. Instead, environmental sensitivity was strongly predicted by what part of the environment was used during the preceding exploration behavior assays. Thus, in juvenile wild starlings, behavioral traits other than the speed of exploration behavior better predicted environmental sensitivity. These results suggest that the relevance of exploration behavior as a personality trait may not be easily generalized across species. Furthermore, although unrelated to exploration speed, this study illustrates how environmental sensitivity correlates with well-known personality traits and thus further highlights how animal personalities can limit behavioral phenotypic plasticity in wild populations.

Who Cares? Between-group variation in alloparental caregiving in sperm whales

Gero, S., Engelhaupt, D., Rendell, L., Whitehead, H. — Tue, 14 Jul 2009 00:07:55 PDT

Although the details of the various systems of allocare in primates, rodents, and carnivores have been well described, little is known about the existence of alloparental care in cetaceans. It is believed that the matrilineal social organization of the sperm whale functions to provide vigilant allomothers for calves at the surface while mothers make deep dives for food. Sperm whale females do have a system of allocare, but details are unknown. This study aimed to elucidate sperm whale allocare, in particular: who escorts whose calf and whether or not calves suckle from nonparent females. Using photo identification and behavioral calf follows, we examined patterns of adult–infant interactions for 23 sperm whale calves in the Sargasso and Caribbean Seas. Although multiple individuals of both sexes escorted the calves, the system of escorting differed between the 2 sites. For all calves studied in the Caribbean, we found that 1 female provided most of the allocare but did not nurse the calf, whereas in the Sargasso, multiple females provided care for, and nursed, the young. We discuss differences between populations that may have resulted in the observed differences in these 2 systems of allocare and how these findings fit with current hypotheses on the roles of kin selection and reciprocal altruism in cooperative care in mammals.

Variation in dominance hierarchies among group-living animals: modeling stability and the likelihood of coalitions

Broom, M., Koenig, A., Borries, C. — Tue, 14 Jul 2009 00:07:55 PDT

Dominance hierarchies based on resource holding potential (RHP) or age are central to the social structure of many group-living animals. Nonhuman primate females and some other mammals are unusual because ranks can depend on kin support or follow an inverse age-graded pattern independent of kin. Whereas the former hierarchies are mediated by frequent coalitions leading to long-term stability, the latter are unstable due to individualistic contests and occasional revolutionary coalitions. We use mathematical modeling to investigate this variation, based on the interaction of triads, subgroups of the group consisting of 3 individuals. This produces 4 key situations, namely that relationships can be either stable or unstable, and involving coalitionary support or not. Varying the parameter values of our model and applying it to real-world examples, we conclude that the emergence of different dominance hierarchies depends on 6 major factors. In addition to RHP, reproductive skew and demography often suggested previously, we stress the importance of 1) the variance in relatedness; 2) the costs and likelihood of interventions; and 3) the value of resources and rank in different life stages, which might be tightly linked to the life history of a species.

Condition-dependent mate choice and its implications for population differentiation in the wolf spider Pirata piraticus

Eraly, D., Hendrickx, F., Lens, L. — Tue, 14 Jul 2009 00:07:55 PDT

When populations face different environmental conditions, both local adaptation and phenotypic plasticity may cause interpopulation divergence of behavioral or phenotypic properties on which mate choice is based. If sustained, this may result in genetic differentiation even in the presence of extant gene flow. Condition dependence of mate choice is one of the main mechanisms explaining these environmental effects. We tested whether experimental food stress affects mate choice in male and female Pirata piraticus spiders from one heavily polluted and one unpolluted reference population. Compared with control females, food-stressed females from the reference population showed a decreased probability of copulation and preferred smaller mates. Females from the polluted population, in contrast, did not show a significant response to food stress and showed size-assortative mating, most strongly under food stress. We explain these results in 2 complementary ways. First, spiders from populations that are not adapted to cope with stress may be less willing to mate when eggs are not fully matured. Second, food-deprived females may show a larger responsiveness toward smaller males because the latter resemble prey more and hungry females tend to attack moving objects more often. Results from this study support the prediction that variation in body condition, driven by local ecological factors, may affect mating behavior and may ultimately lead to population divergence in important life-history traits such as body size.

The influence of the acoustic community on songs of birds in a neotropical rain forest

Luther, D. — Tue, 14 Jul 2009 00:07:55 PDT

The efficacy of communication depends on the detection of species-specific signals in background noise that includes other species’ signals. To avoid confusion with each others’ signals, species should partition communication space. I investigated this possibility for the dawn chorus of birds in an Amazonian rain forest. Acoustic censuses at a location in Matto Grosso, Brazil, detected 82 sedentary species of birds that sang frequently during dawn choruses. Eleven features of these species’ songs were analyzed to characterize the acoustic space of this community. The Euclidean distances between species’ songs in this acoustic space were then used to investigate spatial, temporal, and phylogenetic influences on the divergence of songs. Songs of species in the same stratum of the forest and during the same 30-min interval had the most dispersed songs. Songs of congeners and family members were more dispersed than songs of random species. These results indicate that in this complex acoustic environment, species singing at the same place and time partition signal space. These species either choose times and places for singing to minimize acoustic interference from other species or they have evolved different songs to reduce this interference.

Behavior of kestrels feeding on frugivorous lizards: implications for secondary seed dispersal

Padilla, D. P., Nogales, M. — Tue, 14 Jul 2009 00:07:55 PDT

Secondary seed dispersal is a multistep system that includes 2 or more dispersal processes that can increase the distance from which seeds arrive. This phenomenon is relatively common in some habitats of subtropical oceanic islands due to the frequent frugivore–predator interactions found in them. In this study, we describe how the Eurasian Kestrel is an effective disperser of plants in the secondary seed dispersal process, through interaction with frugivorous lizards. Experiments using captive wild kestrels, along with field data, showed that predation of kestrels on lizards leads to a secondary seed dispersal with 2 possible outcomes: 1) most seeds (89%) are not consumed by kestrels because they reject the lizards’ digestive tracts and so receive only the gut treatment of lizards and 2) a small fraction of seeds (11%) appeared inside the kestrel pellets as a result of indirect ingestion by this raptor, thus undergoing double gut treatment. So, 2 different seed dispersal distances may result from this interaction: 1) when the kestrels capture the lizard and transport it to a perch where the seed-containing guts are discarded and 2) when they indirectly ingest a few seeds from lizards, consequently increasing the dispersal distance. Seeds from the Macaronesian plant species Rubia fruticosa were tested, finding that those passed through kestrels had a lower germinability than those that remained inside the rejected lizards’ digestive tracts, which had similar germination rates to those from control plants (uningested seeds). The kestrel can be considered an important and effective long-distance seed disperser due to the high abundance of frugivorous lizards in their diet, their stereotyped consumption behavior, and the effectiveness of their seed dispersal.

Sex-specific parental strategies according to the sex of offspring in the Adelie penguin

Tue, 14 Jul 2009 00:07:55 PDT

In sexually dimorphic species, the sex of the offspring may induce different constraints for parents. At the same time, within pairs, males and females may have conflicting optimal reproductive strategies. As a result, they may adjust their level of parental investment differently according to the sex of the young. In this study, we examined whether Adélie penguin (Pygoscelis adeliae) chicks were sexually dimorphic and whether parents adjusted their parental investment accordingly. Male chicks were on average approximately 10% heavier than female chicks but not larger. Despite the presumed additional cost associated with male chick growth, no fitness cost differences were observed between parents rearing 1 chick whatever its sex: Adult body mass changes and resight rates during the subsequent breeding season were similar. However, the sex of offspring affected the duration of foraging trips during the early guard stage: At this stage, female adults rearing a female chick performed longer foraging trips than female adults rearing a male chick and males rearing either a male or a female chick. We propose that, because female adults present a lower survival rate after a breeding attempt, they are more prone to modify their level of parental investment than male adults. Moreover, the modulation of the foraging behavior by female adults according to the sex of the chick is likely to reduce intraspecific competition at a time when resource availability at sea is not optimal and when food requirement for female chicks may be lower than for male chicks.

Foraging theory and partial consumption in a tardigrade-nematode system

Hohberg, K., Traunspurger, W. — Tue, 14 Jul 2009 00:07:55 PDT

We investigated foraging behavior of a carnivorous eutardigrade, Macrobiotus richtersi, living in soil or fresh water sediments, where the distribution of nematode prey is heterogeneous and where, consequently, the value of information about prey availability should be high. We directly observed diet choice in various mixtures of 2 size classes of nematodes Acrobeloides nanus, A1 (small prey) and A2 (large prey), differing in profitability (biomass divided by handling time) but not in digestive quality. At various prey densities of A2, we measured how much of each prey item was consumed as a function of search time. Additionally, we derived cumulative biomass uptake rates per single A2 prey from 154 complete feeding acts, and we used the marginal value theorem (MVT) to predict optimal residence time and prey exploitation as a function of environmental quality and search time. Macrobiotus richtersi did not preferentially select the more profitable size class A2 but increased its biomass uptake rate by modifying the amount consumed per prey item (partial consumption): when encounter rates were high and there were more high-quality prey, the tardigrade abandoned food more quickly and consumed less biomass per captured prey. We conclude that 1) hungry tardigrades under food-rich or food-limited conditions maximize biomass gain according to MVT and 2) tardigrades differentiate at least 2 prey situations, high supply (at high encounter rates) and low supply (at moderate and low prey densities). 3) Partial consumption, performed under food-rich conditions or by a satiated predator, leads to a reduction of prey numbers up to 3 times as much as under food-poor conditions.

Condition-dependent alternative mating tactics in a sexually cannibalistic wolf spider

Wilgers, D. J., Nicholas, A. C., Reed, D. H., Stratton, G. E., Hebets, E. A. — Tue, 14 Jul 2009 00:07:55 PDT

Condition-dependent male mating tactics often involve high-quality males capitalizing on the outcome of intersexual selection, whereas low-quality males use behaviors that circumvent female choice to achieve copulation. In the wolf spider Rabidosa punctulata, males display 2 distinct mating tactics: 1) "courtship"—consisting of visual and seismic components or 2) "direct mount"—consisting of males grappling/holding females until they assume a copulatory posture. We tested for condition-dependent tactic expression using both field-collected individuals (representing natural variation in body mass and condition) and individuals whose diet we manipulated in the laboratory (representing extreme divergences in body size and condition). Across both natural and diet manipulated individuals, mating tactic was found to be condition dependent; however, the pattern of tactic expression was initially unexpected. Larger males with better body condition primarily adopted a direct mount tactic, whereas smaller males with poorer body condition primarily utilized courtship. Across all males, copulation success tended to be greatest for the direct mount tactic. We suggest that small, poor condition males predominantly utilize the less-successful mating tactic (courtship) in part due to their increased susceptibility to female cannibalism when attempting a direct mount.

Song types, song performance, and the use of repertoires in dark-eyed juncos (Junco hyemalis)

Cardoso, G. C., Atwell, J. W., Ketterson, E. D., Price, T. D. — Tue, 14 Jul 2009 00:07:55 PDT

Song performance encompasses the idea of how physiologically demanding different songs are to sing, and this is thought to reflect the singing ability of individual birds. In the dark-eyed junco (Junco hyemalis), each male has a repertoire of song types, some of which are shared with other males in the population. We used 4 measures of performance, based on trade-offs between song traits, to test if song performance is consistent among the song types making up the repertoire of individual males. We also tested if song types differ consistently in performance regardless of which males sing them. We found low but significant correlations of performance measures among the song types of individual males. This contrasts with highly consistent differences in performance among song types, regardless of which males sing them. We conclude that performance of single song types, as evaluated by trade-off–based measures of performance, gives little information about male singing ability. As song types differ in performance, we asked if males use the song types in their repertoires differently. We found that juncos use higher performance song types during bouts of more motivated singing, as evaluated by the length of songs, suggesting that song types may be preferentially used in different contexts depending on their performance.

Mate choice copying and mate quality bias: different processes, different species

Vakirtzis, A., Roberts, S. C. — Tue, 14 Jul 2009 00:07:55 PDT