Behavioral Ecology Vol. 10 No. 3: 263-269
© 1999 International Society for Behavioral Ecology
Nuptial feeding by male bushcrickets: an indicator of male quality?
Department of Zoology, The University of Western Australia, Nedlands, WA 6907, Australia
Address correspondence to L. W. Simmons. E-mail: lsimmons{at}cyllene.uwa.edu.au
Received 26 February 1998; revised 25 September 1998; accepted 20 October 1998.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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Male bushcrickets transfer a spermatophore at mating that consists of a sperm-containing ampulla and a product of the accessory glands, the spermatophylax, that is consumed by the female during insemination. Male Requena verticalis produce functionally different spermatophores depending on the availability of sexually receptive females. They will maintain high mating frequency by providing a gift sufficient to ensure sperm transfer, or will invest parentally in females when their mating frequency is low. We examined the relationship between male quality and nuptial feeding under conditions where males invest in ejaculate protection or in parental investment. When investing in ejaculate protection, males reduced the quality of the spermatophylax meal by reducing both the concentration of protein and the absolute amount of protein it contained. There was no relationship between male phenotype and gift size or quality. Moreover, we could find no evidence for the recently advanced hypothesis that females can exercise mate choice by interfering with insemination. However, when males were investing parentally, we found a positive association between spermatophylax size and male size, but no relationship between protein content and male size. Males with high levels of fluctuating asymmetry invested more heavily in the nutritional content of their spermatophylaxes than did symmetrical males. Thus, male quality does influence nuptial feeding, but in a manner predicted by a model of indirect fitness benefits from mate choice.
Key words: bushcrickets, fluctuating asymmetry, male quality, mate choice, nuptial feeding, parental investment, Requena verticalis.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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The males of a variety of insect species provide their mates with a food gift during copulation and/or insemination (Thornhill, 1976b
;
Thornhill and Alcock, 1983;
Simmons and Parker, 1989;
Zeh and Smith, 1985). Nuptial
food gifts can include prey items
(Svensson et al., 1990;
Thornhill, 1976a),
regurgitated food (Steele,
1986), the products of male metabolism
(Brown, 1997;
Gwynne, 1997), and even the
male himself (Andrade, 1996;
Sakaluk et al., 1987). Nuptial
feeding by males has been shown to increase the probability of successful
copulation (Sakaluk et al.,
1995; Steele,
1986), as well as the duration of copulation and number of sperm
transferred (Svensson et al.,
1990; Thornhill,
1976a). Consequently, nuptial feeding increases male fitness
through its effects on fertilization success
(Sakaluk, 1986;
Sakaluk and Eggert, 1996;
Thornhill and Sauer, 1991;
Wedell, 1991). Nuptial feeding
is thus thought to have arisen through sexual selection, driven by sexual
conflict over the insemination process. Once established, nuptial feeding has
the potential to become the focus of natural selection for male parental
investment, if the nutrients provided contribute significantly to the
production and fitness of offspring
(Gwynne, 1997;
Simmons and Parker, 1989).
One issue central to theories on the evolution of nuptial feeding concerns
the benefits obtained by females from resisting insemination. It has been
suggested that interference with insemination in species without nuptial
feeding may represent a form of female choice whereby females ensure their ova
are fertilized by males of high quality
(Eberhard, 1996;
Simmons, 1986,
1987). Nuptial feeding may
thus represent an evolved response in males to avoid female discrimination;
males exercise a form of sexual coercion by preoccupying females with nuptial
gifts. Indeed, male scorpion flies and sagebrush crickets use genital clamping
devices to physically coerce inseminations when they are unable to provide or
synthesize nuptial gifts (Sakaluk et al.,
1995; Thornhill and Sauer,
1991). An alternative argument is that, where females obtain
immediate nutritional benefits from nuptial feeding, female choice may select
for increased investment in nuptial gifts by males. However, because females
exercise discrimination after the onset of copulation, through the control of
insemination, immediate benefit models are invalid for the evolution of
nuptial feeding because they require the discriminative behavior of females to
arise in anticipation of the benefit from nuptial feeding that would follow
(Simmons and Parker, 1989).
Immediate benefit models may be relevant if, once established in a population,
variation in nuptial feeding by males can be assessed prior to copulation.
However, such female choice would focus on the probability of copulation,
rather than the degree of insemination. Recently, Sakaluk and Eggert
(1996) have suggested that
post-copulatory female choice in nuptial feeding species may conform to an
indirect benefit model. They suggested that the size of the nuptial gift may
provide the female with an honest indicator of a male's overall fitness. By
terminating insemination immediately on completion of nuptial feeding, females
would ensure that males of superior quality transferred more sperm and so
enhance the paternity of preferred males.
The males of most bushcrickets (Tettigoniidae) and some crickets
(Gryllidae) produce a secretion from the reproductive accessory glands called
a spermatophylax that is attached to the sperm-containing ampulla of the
spermatophore and transferred to the female at copulation
(Boldyrev, 1915). The female
consumes the spermatophylax before removing and consuming the ampulla of the
spermatophore. The longer the duration of spermatophylax consumption, the
longer the ampulla remains positioned in the female's genital opening, and the
more sperm that are transferred to her sperm storage organ
(Reinhold and Heller, 1993;
Sakaluk, 1984;
Simmons and Gwynne, 1991;
Wedell and Arak, 1989).
Comparative studies of bushcrickets show that spermatophylax size and
ejaculate size covary, supporting the general hypothesis that nuptial feeding
in this group has arisen in the context of ensuring insemination
(Vahed and Gilbert, 1996;
Wedell, 1993). The same
relationship occurs within species
(Simmons, 1995c;
Simmons and Kvarnemo, 1997),
and males with larger spermatophores transfer more sperm, thereby gaining
higher paternity than males with small spermatophores
(Gwynne and Snedden, 1995;
Wedell, 1991). Nevertheless,
studies reveal considerable variation in the size of spermatophylaxes within
species and, consequently, in the duration of nuptial feeding before ampulla
removal (Sakaluk, 1984,
1997;
Simmons, 1995b). Sakaluk and
Eggert (1996) and Sakaluk
(1997) argue that variation in
the duration of nuptial feeding and ampulla attachment in the cricket
Grylloides sigillatus is a manifestation of female choice; females
that remove ampulla sooner are proposed to discriminate against males with
small spermatophylaxes because they prematurely terminate insemination.
Nuptial feeding has been intensively studied in the bushcricket Requena
verticalis (Gwynne,
1997). In this species females gain a nutritional benefit from
nuptial feeding in the form of increased fecundity and offspring survival
(Gwynne, 1988a). The
spermatophylax therefore represents a form of paternal investment. However,
males appear capable of adjusting the size of spermatophore components
depending on prevailing reproductive opportunities
(Simmons, 1995c). When female
availability is high, they produce spermatophores in which the size of the
spermatophylax appears, on average, sufficient to feed females just long
enough to achieve insemination (Simmons,
1995b). As in G. sigillatus, however, there is
considerable variation in spermatophylax size and resultant ampulla attachment
duration so that early ampulla removal could constitute a form of
postcopulatory female discrimination
(Sakaluk and Eggert, 1996). In
contrast, when female availability is low, males produce a spermatophylax that
can reach twice the size necessary to ensure insemination
(Gwynne, 1986;
Simmons, 1995c). Increased
nutrient investment when limited by female availability may allow males to
maximize their reproductive success through increased parental investment
(Simmons, 1995c). Because of
increased male investment in nuptial feeding, females are unlikely to retain
the ability to exercise choice via interference with insemination.
Nevertheless, if males vary in their ability to invest parentally, females
could benefit from conventional precopulatory mate choice. Here we examine the
relationship between male quality and spermatophylax quality and the potential
for female choice in this system.
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METHODS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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Animals used in this study were collected from the grounds of the University of Western Australia, Nedlands, Western Australia. Females were collected as penultimate instar nymphs and reared to adulthood in the laboratory. The date of adult eclosion was noted, and all females were used in mating trials once only, when they were between 3 and 11 days of age. Males to be used in mating trials were collected as adults, taken on the basis of their calling activity; males do not call until they are ready to mate (Simmons, 1994
). All animals
were housed in separate containers, provided with a mix of oats, pollen, and
fish flake, and watered daily. Animals were maintained, and experiments
performed, in an experimental room with a reversed light:dark cycle and a
temperature of 25°C.
Manipulating spermatophore morphology
On the day after collection, we provided males with a single virgin female
and allowed them to mate. Males were randomly assigned to one of two remating
treatments. In the first, males were provided with a second female 4 days
after their initial mating. Because males require an average of 4 days to
recover from mating before they will attract and mate with a second female,
this treatment was established to simulate high female availability. In the
second treatment, we isolated males from females for 12 days after their
initial mating, thereby simulating a low female availability. These two
treatments have been shown to influence the morphology of spermatophores
produced by males at their next mating
(Simmons, 1995c). After their
allotted remating interval, males were provided with a second virgin female
and allowed to mate. Immediately after spermatophore transfer (for a detailed
description of mating in this species, see
Simmons, 1994), pairs were
assigned at random to one of two experiments. The first experiment aimed to
establish the relationship between male quality and spermatophore quality,
while the second examined the potential for female choice by interference with
insemination.
Spermatophore quality
Immediately after copulation, we removed the spermatophore from the females
gonopore and separated the ampulla and spermatophylax. The ampulla and
spermatophylax were weighed and the spermatophylax placed into 1 ml of 0.1%
sodium dodecyl sulfate (SDS). Spermatophylaxes were homogenized and left to
dissolve for 3-7 days at 20°C before establishing their protein content
using the dye-binding protein assay, Bio-Rad. We first constructed a standard
assay curve using bovine serum albumin. Preliminary assays of spermatophylax
material revealed that a onefold dilution was required for the absorbence to
fall within the range of the standard curve. Thus, a further 1 ml of SDS was
added to each spermatophylax before vortexing the solution. We performed
protein assays for each spermatophylax in duplicate, or in triplicate if the
first two samples differed in absorbence by >0.02. Protein concentration
was established from the mean absorbence interpolated onto the standard curve
and multiplied by a factor of 2 to account for the dilution.
Male quality
We estimated male quality from morphological aspects of male phenotype. As
in many insects (Thornhill and Alcock,
1983), male body size is a strong predictor of male reproductive
success in bushcrickets. Large males can produce more spermatophores per unit
time and, in natural populations, are more successful in sexual competition
(Schatral, 1990;
Simmons, 1993). Male body size
appears to have a genetic basis (Gwynne,
1988a). Fluctuating asymmetry (FA) is characterized by random
deviations from perfect symmetry in bilaterally paired traits and can be used
as an indicator of environmental and genetic stress
(Palmer and Strobeck, 1992).
Within populations, deviations from symmetry are thought to be indicative of
individual quality (Møller,
1993; Møller and
Pomiankowski, 1993). We thus used measures of both male size and
FA as estimates of male quality. We estimated male size from the length of the
pronotum and measured FA in all three pairs of limbs by measuring the length
of left and right tibiae. All linear measurements were made to the nearest 0.5
ocular unit using an eye-piece graticule in a stereomicroscope.
Leg FA was calculated as the left minus the right value. Our measures of FA were significantly repeatable for all three pairs of legs; repeated-measures ANOVA of signed values of FA showed significantly greater variance between individuals than between measures of the same individual (fore tibia F17,18 = 2.60, p =.026; mid-tibia F16,17 = 2.72, p =.024; hind tibia F17,18 = 5.93, p =.002). However, the mean signed asymmetry of fore tibia was significantly different from zero (t = 3.19, df = 49, p =.003), and the asymmetry values for mid-tibia were not normally distributed (Filliben's r =.970, n = 50, p <.05). We therefore rejected the hypothesis that fore and mid-tibia exhibited FA. Signed values of asymmetry for hind tibia were normally distributed (Filliben's r =.980, n = 53, p <.1) about a mean of zero (t = 1.01, df = 52, p =.317), indicative of true FA. Thus we used the absolute value of FA in hind tibia as an indicator of male quality.
Insemination success
The process of sperm transfer and spermatophylax consumption was examined
using a combination of manipulated and unmanipulated matings. After
spermatophore transfer, we removed males from the mating enclosure, taking
care not to disturb the female. Females were randomly assigned to 1 of 6
treatments. In the first five treatments, ampullae were removed experimentally
after periods ranging from 30 to 180 min. In the final treatment, females were
allowed to remove their own ampullae after completion of the spermatophylax
meal. For manipulated females, the ampulla of the spermatophore was removed
after the allotted attachment time and the ampulla and female frozen for later
sperm counts. For unmanipulated females, the time from spermatophore transfer
until the female reached back to remove the spermatophylax was recorded. The
duration of spermatophylax consumption was recorded as the time from
spermatophylax removal until no traces of the spermatophylax remained on the
females' mandibles, and females began to clean their antennae and/or front
limbs (see Simmons, 1995b). We
recorded the time from completion of the spermatophylax meal until the female
began to remove the ampulla. As soon as the female reached to grasp the
ampulla, she was disturbed, and the ampulla was removed with forceps. Both
female and ampulla were frozen for later sperm counts.
We dissected females and removed the sperm storage organ (spermatheca) and placed it into a known volume of particle-free water. The spermatheca was ruptured and a homogenous mix of its contents made by constant mixing. Serial dilutions were made dependent on the expected numbers of sperm (determined from preliminary sperm counts from nonexperimental females). Known aliquots of solution were placed onto cleaned glass slides and allowed to air dry. Sperm counts were made under dark-field phase contrast. We counted six samples for each female and used the mean count as an estimate of the number of sperm transferred to the spermatheca. Ampullae were similarly reptured in particle-free water and sperm samples processed as for spermathecal samples. We calculated the total number of sperm ejaculated by a male as the sum of the sperm contained in the spermatheca of the female and remaining in the ampulla. The percentage of sperm transferred was thus determined for each manipulated and unmanipulated female.
Throughout statistical analyses, data were assessed for normality, and nonparametric tests were used whenever data could not be normalized by transformation. Nonparametric statistics were also used for FA analyses because absolute values of FA have a characteristic half-normal distribution.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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Spermatophore morphology varied in accord with our manipulation of male remating interval; males that mated after 4 days had smaller ampullae and smaller spermatophylaxes compared with males that mated after 12 days (Table 1). Spermatophylax quality also varied significantly between groups; controlling for spermatophylax size, males mating after 4 days produced spermatophylaxes with a significantly lower concentration of protein, weight for weight, and so provided absolutely less protein than did males mating after 12 days (Table 1).
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Associations between male quality and spermatophore quality
Larger males produced larger sperm-containing ampullae under both remating
intervals (Figure 1A). However,
there was a positive association between male size and the size of the
spermatophylax meal only when males were held for 12 days between matings
(Figure 1B). The degree of FA
did not influence the size of the ampulla or spermatophylax meal for either
4-day (ampulla: rs = -.002, Z = -0.01, p
=.992, n = 26; spermatophylax: rs = -.01,
Z = -0.03, p =.977, n = 26; all values corrected
for ties) or 12-day (ampulla: rs = -.24, Z =
-1.71, p =.242, n = 25; spermatophylax:
rs = -.16, Z = -0.770, p =.440,
n = 25) remating intervals.
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Male size had no influence on the quality of the spermatophylax meal; neither the absolute mass of protein in the spermatophylax nor the concentration of protein were related to male body size for either remating interval treatment (4 days: protein content, F1,27 = 1.56, p =.223; % protein, F1,27 =.08, p =.777; 12 days: protein content, F1,26 =.13, p =.716; % protein, F1,26 = 2.41, p =.133). However, there was a significant positive association between the levels of FA and spermatophylax quality when males mated after 12 days; the spermatophylaxes of asymmetrical males had a greater concentration of protein (Figure 2A) and contained a greater absolute mass of protein than those of symmetrical males (Figure 2B). Spermatophylax quality was not associated with FA when males mated after 4 days (Figure 2).
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Insemination success
Males mating after 4 days transferred fewer sperm in total than did males
mating after 12 days (4 days, 1.09±0.11 million; 12 days,
1.63±0.17 million, t = 2.41, df = 39, p =.021). In
experimental manipulations, the proportion of sperm transferred from the
ampulla increased across the five attachment duration treatments, but there
was no influence of male remating treatment, and no significant interaction
(Kruskal-Wallis, remating interval 
2H = 0.76, df =
1, p =.402; ampulla attachment, 2H =
20.41, df = 3, p <.001; interaction 2H
= 0.77, df = 3, p =.858). However, we note that the smaller ejaculate
produced by males after 4 days tended to be transferred at a higher rate than
did the larger ejaculates of males mating after 12 days
(Figure 3). There were no
significant differences between male remating intervals in the time taken for
females to remove the spermatophylax meal from the ampulla (4 days,
182.7±19.8 s, n = 18; 12 days, 162.0±19.7 s, n
= 11; Mann-Whitney U = 87, ns) or in the time taken to remove the
ampulla after completion of the spermatophylax meal (4 days, 11.2±3.8
min, n = 11; 12 days, 6.9±1.4 min, n = 9;
Mann-Whitney U = 52, ns). The time taken for females to consume the
spermatophylax during unmanipulated matings was significantly longer for males
mating after 12 days (t = 3.73, df = 19, p =.001). However,
no spermatophylax consumption time was short enough to prevent complete
transfer of the ejaculate (see Figure
3); the mean proportion of sperm transferred during unmanipulated
matings did not differ between male remating treatments (4 days,
0.998±0.008, n = 7; 12 days, 0.999±0.001, n =
5; Mann-Whitney U = 7, ns).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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Variation in spermatophore morphology found in our experiments is consistent with that reported by Simmons et al. (1992
) and Simmons
(1995c); male R.
verticalis appear to adjust the function of their spermatophores
depending on the availability of females. With high mating frequency, males
transferred a spermatophore with a spermatophylax meal that was of a size just
sufficient to ensure sperm transfer
(Simmons, 1995b). When mating
frequency was low, however, they increased their investment in the female,
providing a spermatophylax meal that was twice the size necessary to
facilitate sperm transfer, and an enlarged ejaculate that ensures paternity
for nurturant males (Gwynne,
1988b; Simmons,
1995c). Moreover, our analyses show that spermatophylax meals
varied in quality as well as in size; when males invested parentally, they
increased the concentration of protein contained within the spermatophylax,
and so increased the total amount of protein supplied to the female. Previous
work suggests that these differences in spermatophore morphology reflect
adaptive plasticity in male behavior, rather than physiological constraints
imposed by male mating history (Simmons,
1995c). Nourishment obtained by female R. verticalis
through spermatophylax feeding has been shown to increase the number and
fitness of offspring produced (Gwynne,
1988a). Thus, males appear capable of making fine adjustments to
the structure of their spermatophores, investing in sperm transfer when the
potential for multiple mating is high and in parental investment when the
potential for multiple mating is low. We can therefore use our results to test
predictions concerning the relationship between male quality and nuptial
feeding when nuptial gifts function either in the context of mating effort or
parental investment.
Male quality and mating effort
When nuptial feeding functions to ensure insemination, Sakaluk and Eggert
(1996) and Sakaluk
(1997) have argued that
variation in the duration of nuptial feeding may facilitate cryptic female
choice, in that males with shorter feeding, and thus shorter ampulla
attachment duration, will have reduced sperm transfer. They suggest that the
spermatophylax of G. sigillatus may represent an honest signal of
male quality allowing females to bias insemination toward males with larger
spermatophylaxes. However, neither Sakaluk and Eggert
(1996) or Sakaluk
(1997) provide data on sperm
transfer. The demonstration of cryptic female choice requires evidence that
females actually influence sperm transfer by ampulla removal. The size of
ejaculates transferred to females may represent an adaptive male strategy
rather than a female one (Gage,
1991), so it must be shown that female behavior affects the
proportion of a male's ejaculate transferred; smaller spermatophylaxes may
function perfectly well in ensuring the transfer of smaller ejaculates.
It must also be shown that spermatophylax size is an indicator of male
quality. Our data show that, when males invest in ejaculate protection,
spermatophylax size and quality are not indicative of male quality;
spermatophylax size and protein content were not related to male size or to
the levels of FA. Likewise, Eggert and Sakaluk
(1994) failed to find a
relationship between male quality, estimated from the levels of FA in the
forewings, and spermatophylax size for G. sigillatus. Our data for
R. verticalis also show that, despite considerable variation in
spermatophylax consumption and ampulla attachment times (see also
Simmons, 1995b), males always
achieved complete sperm transfer, even when the spermatophylax functioned as
an ejaculate protector, as it does in G. sigillatus
(Sakaluk, 1984). Ampullae
varied in weight across our male remating treatments by 20% and sperm numbers
by 30%, yet the time required for complete sperm transfer did not vary. These
data show that variation in ampulla attachment has no influence on sperm
transfer for R. verticalis. Gage and Barnard
(1996) have shown that male
G. sigillatus increase ampulla weight and sperm number in response to
the risks of sperm competition. The fact that spermatophylax size is not
similarly increased suggests that, like R. verticalis, increased
ampulla attachment duration is not required for the transfer of larger
ejaculates. We thus find little support for the notion that nuptial feeding in
the context of ejaculate protection provides an avenue for cryptic female
choice.
Male quality and parental investment
When males invested in spermatophylax meals of increased size and
nutritional value, we found a significant positive association between male
size and the size of the spermatophylax meal. Nevertheless, larger males did
not transfer greater amounts of protein, so there would be no immediate
benefit for females from mating preferentially with larger males. Similarly,
large males are unlikely to gain parentally from providing a larger
spermatophylax because they are not increasing their nutrient contribution to
their offspring. We have shown that, when males are investing parentally,
spermatophylax size plays no role in sperm transfer, so there are unlikely to
be any direct benefits in sperm competition for larger males providing larger
spermatophylaxes. This leaves us with the possible interpretation that large
males signal their phenotypic quality to females via the larger
spermatophylax. Such an interpretation would only be supported if females
exercised some form of differential reproductive investment (sensu
Burley, 1988) following matings
with larger males. Currently we have no data to address this issue.
The relationship between paternal provisioning and male quality is complex.
Recent studies suggest that in species where both males and females provision
offspring and/or provide parental care, attractive males tend to invest less
in offspring than unattractive males so that females pay a cost for proposed
indirect benefits of mating with attractive males. Thus, in an experiment in
which the sexual traits of male barn swallows, Hirundo rusticus, had
been experimentally manipulated, Møller
(1994) found that males with
shortened tails had an increased number of feeding visits to the nest, as did
males in which the levels of FA in tail length had been increased. Moodie and
Moodie (1996) similarly found
that asymmetrical male sticklebacks hatched a greater number of fry than did
symmetrical males, suggesting that they invested more heavily in egg defense
than did symmetrical males. Møller and Thornhill
(1998) have recently suggest
that in general, the interaction between sexual selection and parental
investment should yield two prediction: (1) where secondary sexual traits
signal male parental investment, male contribution to offspring production
should be positively associated with the expression of the sexual trait, and
(2) where sexual traits reflect male quality, males of high quality should
provide a relatively lower investment in offspring because they can increase
their reproductive success through mating effort. A review of the literature
on species with biparental care provided general support for the proposed
dichotomy.
We found that male R. verticalis with high values of FA invested
more heavily in the nutritional value of spermatophylax meals, providing a
greater total amount of protein than males with low values of FA. Studies of
developmental stability have show that asymmetrical individuals often have a
lower mating success and lower longevity than symmetrical individuals (e.g.,
Harvey and Walsh, 1993;
Møller, 1996;
Møller et al., 1996;
Simmons, 1995a;
Simmons and Ritchie, 1996;
Ueno, 1994). We have shown
that, on average, male R. verticalis with low mating frequency
increase parental investment via nuptial feeding. Increased investment in the
nuptial gift by males with a lower than average expected mating success may
represent an alternative route to reproductive success, given that the amount
of resources provided to females is positively associated with the number and
survival of offspring produced (Gwynne,
1984, 1988a).
Moreover, following the arguments of Møller and Thornhill
(1998), our data are
consistent with the spermatophylax gift representing a potential cue to
indirect fitness benefits for females, given the positive association between
male size and gift size and the negative association between male quality and
nutritional investment in the gift. The relationship between male size and
spermatophylax size and the possibility of female choice via differential
reproductive investment warrants further study.
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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We thank Kylie Gaull for assistance in collecting animals and Anders Møller for comments on the manuscript. This work was supported by funds from the Australian Research Council.
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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