Behavioral Ecology - Advance Access

Long tails matter in sugarbirds--positively for extrapair but negatively for within-pair fertilization success

Thu, 05 Nov 2009 07:53:13 PST

Extrapair mating is known to occur in many animals and potentially has a significant influence on reproductive success. Female extrapair mate choice may explain the occurrence of exaggerated ornaments in socially monogamous species, but the influence of ornamentation on extrapair mating success has rarely been investigated experimentally. Cape sugarbirds (Promerops cafer) are socially monogamous, almost always lay 2 egg clutches and have long-term pair bonds often lasting several seasons. However, they also display sexually dimorphic extravagant ornamentation in the form of a long, graduated tail and have one of the highest rates (65% of young) of extrapair paternity recorded in birds. We provide a test of the hypothesis that the ornamented tail is used in mate choice for extrapair partners by conducting an experiment in which tail length was manipulated after social mating but before copulation. This experiment therefore allowed females to respond to the manipulation of male tail length when making a choice of copulation partner but not social mate. We show that the tail length of male sugarbirds has a significant effect on the success of males in gaining extrapair paternity, with long-tailed males obtaining significantly more extrapair young than short-tailed males. However, males with short tails sire a significantly greater proportion of the nestlings in their own nests than long-tailed individuals. This result suggests that males may adopt alternative strategies dependent on their ornamentation.

Predator escape tactics in birds: linking ecology and aerodynamics

van den Hout, P. J., Mathot, K. J., Maas, L. R. M., Piersma, T. — Thu, 05 Nov 2009 07:53:12 PST

In most birds, flight is the most important means of escape from predators. Impaired flight abilities due to increased wing loading may increase vulnerability to predation. To compensate for an increase in wing loading, birds are able to independently decrease body mass (BM) or increase pectoral muscle mass (PMM). Comparing nearshore and farshore foraging shorebird species, we develop a theory as to which of these responses should be the most appropriate. We hypothesize that nearshore foragers should respond to increased predation by increasing their PMM in order to promote speed-based escape. Instead, farshore foragers should decrease BM in order to improve agility for maneuvering escape. Experiments on 2 shorebird species are consistent with these predictions, but on the basis of the theoretical framework for evaluating effect size and biological significance developed here, more experiments are clearly needed.

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

Aronsson, M., Gamberale-Stille, G. — Mon, 02 Nov 2009 04:57:00 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.

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

Murphy, T. G., Rosenthal, M. F., Montgomerie, R., Tarvin, K. A. — Mon, 02 Nov 2009 04:56:59 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.

Changing philosophies and tools for statistical inferences in behavioral ecology

Mon, 02 Nov 2009 11:56:29 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.

Reduced extrapair paternity in response to experimental stimulation of earlier incubation onset in blue tits

Fri, 30 Oct 2009 06:15:13 PDT

Although the causes and consequences of extrapair paternity (EPP) have been studied extensively in birds, little is known about the regulation of extrapair copulation (EPC) behavior and how it may tie in with other aspects of avian reproduction. In birds, the presence of eggs stimulates incubation and, subsequently, the cessation of egg production. We propose that the same mechanism also regulates female motivation to engage in EPCs. To test this idea, we simulated the earlier onset of laying in blue tits (Cyanistes caeruleus), by adding model eggs to nests before natural laying commenced. Most females accepted these eggs, covering them with nest material in the natural way. As predicted, these broods hatched more asynchronously than control broods, revealing an earlier onset of incubation, and were less likely to contain extrapair offspring (EPO) suggesting that stimulation from eggs also inhibits motivation to seek EPCs. Egg stimulation is thought to cause cessation of laying a fixed number of days before clutch completion, after a certain hormonal threshold is exceeded. Similarly, a lower threshold may inhibit engagement in EPCs relative to clutch completion, explaining the proportional increase in EPO toward the extremes of clutch size, which we also observed, and would be consistent with a fertility or compatibility insurance function for EPCs. Our findings may represent the best experimental evidence for female-mediated effects on the timing of EPCs and suggest how EPP may be integrated within the regulatory mechanism of avian reproduction.

Sex matters: a social context to boldness in guppies (Poecilia reticulata)

Tue, 27 Oct 2009 11:15:16 PDT

Boldness is a key element of behavioral variation in animals. Many studies have shown variation between individuals in their propensity to take risks across a wide range of taxa, yet surprisingly few studies have investigated the importance of social context in influencing an animal's boldness. Here, we focus on the role that the sex composition of a social group plays in individual boldness in a sexually dimorphic species, the Trinidadian guppy (Poecilia reticulata). We predict that after exposure to a simulated aerial predator, male guppies should be bolder in the presence of females compared with males to maximize their mating opportunities. Furthermore, we predict that female guppies will adopt riskier behavior when shoaling with males in an effort to avoid sexual harassment. Using a model avian predator, we tested these hypotheses and found evidence to support our second prediction but not our first. Specifically, we found that male guppies returned to movement more rapidly after a fright response when shoaling with males than with females. Female focal fish in contrast returned to movement significantly quicker when shoaling with males than females. Also, we found a significant correlation in boldness across social contexts (a behavioral syndrome) in male but not female fish. This study highlights the importance of social context for individual boldness and suggests that for risk-averse behavior in social, sexually dimorphic species, sex matters.

Cleaning in pairs enhances honesty in male cleaning gobies

Soares, M. C., Bshary, R., Cote, I. M. — Thu, 22 Oct 2009 04:48:13 PDT

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.

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

Chan, R., Stuart-Fox, D., Jessop, T. S. — Thu, 22 Oct 2009 04:48:12 PDT

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.

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

Hunter, J. S. — Wed, 21 Oct 2009 04:50:42 PDT

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.

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

Rebar, D., Bailey, N. W., Zuk, M. — Wed, 21 Oct 2009 04:50:42 PDT

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.

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. — Wed, 21 Oct 2009 04:50:40 PDT

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.

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

Ward, J. L., McLennan, D. A. — Wed, 21 Oct 2009 11:21:01 PDT

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.

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

Ferrari, M. C.O., Chivers, D. P. — Mon, 12 Oct 2009 02:51:47 PDT

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.

Prevalence of avian influenza and sexual selection in ducks

Hegyi, G., Moller, A. P., Eens, M., Garamszegi, L. Z. — Mon, 12 Oct 2009 02:51:46 PDT

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.

Learned conspecific mate preference in a species pair of sticklebacks

Kozak, G. M., Boughman, J. W. — Wed, 07 Oct 2009 08:06:13 PDT

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.

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. — Wed, 07 Oct 2009 08:06:10 PDT

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.

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

Hu, Y., Cardoso, G. C. — Wed, 07 Oct 2009 08:06:07 PDT

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.

Trait duplication by means of sensory bias

Rodriguez, R. L. — Sun, 04 Oct 2009 19:30:06 PDT

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

Segoli, M., Keasar, T., Harari, A. R., Bouskila, A. — Wed, 23 Sep 2009 06:36:49 PDT

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.

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

Nunes, A. C., Mathias, M. d. L., Ganem, G. — Thu, 03 Sep 2009 11:16:08 PDT

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.

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, 03 Sep 2009 11:16:08 PDT

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.

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

Aisenberg, A., Eberhard, W. G. — Tue, 25 Aug 2009 07:12:54 PDT

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.

The educated prey: consequences for exploitation and control

Bischof, R., Zedrosser, A. — Mon, 24 Aug 2009 06:26:21 PDT

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.

Environment-dependent use of mate choice cues in sticklebacks

Heuschele, J., Mannerla, M., Gienapp, P., Candolin, U. — Wed, 19 Aug 2009 10:16:32 PDT

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.

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

Rieucau, G., Giraldeau, L.-A. — Wed, 19 Aug 2009 10:16:31 PDT

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.

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

Murray, C. M., Lonsdorf, E. V., Eberly, L. E., Pusey, A. E. — Wed, 19 Aug 2009 10:16:31 PDT

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.

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

Coker, D. J., Pratchett, M. S., Munday, P. L. — Wed, 19 Aug 2009 10:16:30 PDT

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.

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. — Tue, 18 Aug 2009 12:16:21 PDT

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.

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

Muck, C., Kempenaers, B., Kuhn, S., Valcu, M., Goymann, W. — Wed, 12 Aug 2009 06:07:26 PDT

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.

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

Leonard, A. S., Hedrick, A. V. — Wed, 12 Aug 2009 06:07:26 PDT

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.

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

Latty, T., Beekman, M. — Wed, 12 Aug 2009 06:07:25 PDT

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. — Wed, 12 Aug 2009 06:07:25 PDT

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.

Female tungara frogs vary in commitment to mate choice

Baugh, A. T., Ryan, M. J. — Tue, 11 Aug 2009 06:31:33 PDT

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.