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1.
Sperm competition or sperm selection: no evidence for female influence over paternity in yellow dung flies Scatophaga stercoraria 总被引:2,自引:0,他引:2
L. W. Simmons P. Stockley R. L. Jackson G. A. Parker 《Behavioral ecology and sociobiology》1996,38(3):199-206
Recent studies of non-random paternity have suggested that sperm selection by females may influence male fertilization success.
Here we argue that the problems originally encountered in partitioning variation in non-random mating between male competition
and female choice are even more pertinent to interpreting patterns of non-random paternity because of intense sperm competition
between males. We describe an experiment with the yellow dung fly, Scatophaga stercoraria, designed to partition variance in the proportion of offspring sired by the second male, P
2, between males and females, and to control for sperm competition. Large males were shown to have a higher P
2 than small males but P
2 was independent of the size of the female’s first mate. This result might suggest an absolute female preference for large
males via sperm selection. However, large males have a higher constant rate of sperm transfer and displacement. After controlling
for this effect of sperm competition, large males did not achieve higher paternity than small males. We argue that a knowledge
of the mechanism of sperm competition is essential so that male effects can be controlled before conclusions are made regarding
the influence of sperm selection by females in generating non-random paternity.
Received: 4 April 1995 / Accepted after revision: 17 October 1995 相似文献
2.
Genetic variation and covariation during larval and juvenile growth in Mercenaria mercenaria 总被引:1,自引:0,他引:1
Quantitative genetic variances and covariances were estimated for shell length of the hard clam Mercenaria mercenaria (L.) at three larval stages (prodissoconch I, 2 d and 10 d post-fertilization) in 1987 and in 1988 after ca. 9 mo of growth. At each sample interval additive genetic variance was a highly significant component of the total size variation. Narrow sense heritability estimates for shell length ranged between 0.58 (±0.10) for prodissoconch I and 1.08 (±0.29) for 2-d-old larvae. There was significant and positive genetic covariance in prodissoconch I and 2-d larval shell length which resulted in a highly significant genetic correlation (r
g=0.74) between these two traits. This covariance is not surprising since the prodissoconch I comprises the majority of the larval shell of a 2-d-old larvae. The genetic covariances between 2-d-old and 10-d-old larvae and between 10-d-old larvae and 9-mo-old juveniles were low and not significantly different from zero. These results indicate that there is substantial genetic variation for shell growth in M. mercenaria but this variation is not stable during development; the genetic variation in shell growth at one stage of development is not strongly related to the genetic variation in growth during other ontogenetic periods. In this study there were no evident constraints to natural selection for increased shell growth rate during development, which coupled with the high levels of genetic variation may suggest that in nature high rates of larval growth may not be normally subject to significant selective pressure. 相似文献
3.
Sperm competition is predicted to generate opposing selection pressures on males. On one hand, selection should favour ‘defensive’ adaptations that protect a male’s ejaculate from displacement, while, on the other hand, selection should favour ‘offensive’ adaptations that overcome paternity assurance mechanisms of rivals. Here, we use the sterile male technique to assess sperm precedence when a male dung beetle Onthophagus taurus mates in both a defensive (first male) and an offensive (second male) role. Significant variation in a male’s sperm precedence (both P
1 and P
2) was detected, and an individual’s defensive (P
1) and offensive (P
2) abilities were positively correlated. Thus, it appears that sexual selection simultaneously selects for ‘defensive’ and ‘offensive’ adaptations in O. taurus. We discuss a variety of male traits in O. taurus that potentially contribute to a male’s ability to be successful when mating in an ‘offensive’ and a ‘defensive’ role. 相似文献
4.
Bicer BT Sakar D 《Journal of environmental biology / Academy of Environmental Biology, India》2010,31(5):667-669
A 4 x 4 full-diallel cross was studied to estimate the gene effects and genetic parameters of pod and seed traits. According to Hayman's method, additive genetic variance was significant for pod length and seed length and width, also, both additive and dominance genetic variance were significant for pod thickness and width. As additive gene effects were significant for pod and seed traits, it is suggesting the selection of this traits early generations. Partial dominance was important for traits. The high narrow sense heritability of pod and seed traits was between 86 and 97%. 相似文献
5.
Merja Otronen 《Behavioral ecology and sociobiology》1998,42(3):185-191
The significance of male asymmetry in postcopulatory sexual selection was studied in the fly Dryomyza anilis by examining whether male asymmetry is related to fertilization success. The traits measured were wing length, tibia length
and the length of small and large claspers. The male claspers are situated at the tip of the abdomen, functional pair of claspers
consists of a large and a small clasper on the same side of the body. These claspers are used to tap the female abdomen after
sperm transfer, which has been shown to increase fertilization success for the mating male. Fertilization success was negatively
related to the fluctuating asymmetry of wing length, suggesting either female preference for more symmetrical males or a relationship
between male asymmetry and intrasexual selection which was reflected in mating performance. Fertilization success was also
related to the length of small claspers, decreasing with increasing length of the claspers. In addition, males with asymmetrical
small claspers enjoyed higher fertilization success than symmetrical ones. This study shows that fluctuating asymmetry in
wing length is an important fitness trait in postcopulatory sexual selection. Since male tapping affects sperm distribution
in the female's sperm storage organs, the higher fertilization success of males with asymmetrical small claspers could have
a functional relationship with the asymmetrical position of female sperm storage organs.
Received: 6 March 1997 / Accepted after revision: 8 November 1997 相似文献
6.
Tom Tregenza Fathi Attia Saleh Salem Bushaiba 《Behavioral ecology and sociobiology》2009,63(6):817-823
Differences among males in their success in achieving fertilisations when females mate with more than one partner are now
recognised as an important target of sexual selection. However, very few studies have attempted to determine whether particular
males are consistently successful in sperm competition and whether success in sperm competition is a heritable trait. Additionally,
the potential heritability of female traits that influence the outcome of sperm competition has received only limited attention.
Using the polyandrous beetle Tribolium castaneum, we examined repeatability of male success in sperm competition by mating pairs of males carrying different visible genetic
markers to a string of different females. Males showed consistency in their ability to successfully transfer sperm to females,
but not in their success in sperm competition. Furthermore, when we independently compared success in sperm competition of
fathers with their sons, we found no evidence for heritability of this trait. Similarly, females that exhibited high or low
first male sperm precedence did not tend to have daughters that showed the same pattern. Our results suggest that we should
be wary of assuming that success in sperm competition is heritable through either sex. 相似文献
7.
Sperm traits often show extreme variation both between and within species. Between-species variation may often be interpreted
in the context of a sperm competition theory, but within-species variation has remained unexplained. Previous studies on intraspecific
variation in sperm traits have focused on a limited set of variables and may have failed to explain observed variation because
of potential trade-offs between different sperm traits. We report on variation in number, size, motility and longevity of
sperm in the frog Crinia georgiana, a species where sperm competition is common. We found intrapopulation variation in sperm size and motility and interpopulation
variation in relative sperm number and size. When we combined relative sperm number and size into one variable, and motility
and longevity into another, we found significant interpopulation variation in these variables as well. We also detected considerable
intra- and significant interpopulation variation in cumulative sperm quality, a combination of all four sperm traits. Furthermore,
a significant effect of the interaction between population origin and male size on sperm characteristics indicated interpopulation
variation in the strength of selection acting on sperm traits of males adopting different mating strategies. We discuss heterogeneity
in the reproductive environment, a complex genetic background in the determination of sperm characteristics and varying levels
of developmental noise as potential contributors to the observed variation in sperm traits. 相似文献
8.
Independence, not conflict, characterizes dart-shooting and sperm exchange in a hermaphroditic snail
Although the sexes are united in hermaphrodites, conflict can still occur because the male and female functions have separate
interests. We examined the evidence for conflict in the mating system of the terrestrial snail Cantareus aspersus (formerly Helix aspersa) where sharp, calcareous darts are ‘shot’ during courtship. We predicted that the use of the dart would either reflect or
create conflict and this would be evident in either the courtship behavior or the transference of sperm. Previous studies
demonstrated that the dart functions after sperm transfer to increase sperm survival. Using detailed observations of mating
snails, we examined the factors that determine dart shooting order, the behavioral responses after being hit by a dart, the
accuracy of dart shooting, and the allocation of sperm resources. We found that each dart was shot independently, and each
animal appeared to be interested only in getting off the best possible shot, probably one that penetrates deeply near the
genital pore. There is no evidence of mating conflict. Every snail transfers sperm to its partner, and the size of the donation
does not depend on the success or failure of either snail’s dart shot. Although the receipt of a dart does not appear to cause
harm, it may produce indirect costs due to the partial loss of control over fertilization. We conclude that mating in C. aspersus is a partnership in which independent actors demonstrate unconditional reciprocity during courtship and sperm transfer. 相似文献
9.
According to indicator models of sexual selection, mates may obtain indirect, i.e. genetic, benefits from choosing partners indicating high overall genetic quality by honest signals. In the scorpionfly Panorpa vulgaris, both sexes show mating preferences on the basis of the condition of the potential partners. Females prefer males that produce nuptial gifts (i.e. salivary secretions) during copulation, while males invest more nuptial gifts in females of high nutritional status. Both characters, males' ability to produce nuptial gifts and high nutritional status of females, are known to be reliable indicators of foraging ability. Thus, besides possible direct benefits, both sexes might also obtain indirect benefits in terms of “good foraging genes” by their choice and thereby increase the fitness of their offspring. A prerequisite for this possibility is the heritability of the respective trait. In the present study, we estimated the repeatability and the heritability of foraging ability. Our results indicate (1) a significant repeatability of individual foraging efficiencies in males and females and (2) a heritable component of this trait by a significant parent–offspring regression. These findings suggest that genetic benefits in terms of increased offspring foraging ability might contribute to selection for mating preferences in both sexes. 相似文献
10.
Immigration into locally adapted populations has been suggested, among other potential causes, to maintain genetic variance in fitness necessary for good-genes models. Using a reciprocal transplant experiment we examined whether females prefer native to transferred males in the grasshopper Chorthippus biguttulus. On average, native and transferred males did not differ in their attractiveness, measured as female response rate to playbacks of male acoustic courtship signals. In line with this result, we found no significant effect of transfer on body size, condition, fluctuating asymmetry or song traits. However, the reciprocal transplant experiment showed that environmental conditions did influence body condition and maximum loudness of the calling song, but that the genetic origin of male grasshoppers had no significant effect on any of the analysed traits.Communicated by L. Simmons 相似文献
11.
Family insurance: kin selection and cooperative breeding in a solitary primate (Microcebus murinus) 总被引:1,自引:0,他引:1
Lactation imposes substantial physiological costs on mothers and should therefore not be directed towards foreign offspring. Such allonursing, however, is common in mammal species that share roosts. Hypotheses to explain allonursing among such plural breeders include misdirected parental care, milk evacuation, brood parasitism, reciprocity, and kin selection. The necessary behavioral data, in combination with data on kinship and kin recognition, have rarely been available to distinguish among these explanations, however. In this study, we provide evidence for cooperative nursing and adoption by plural-breeding females in a nocturnal primate, the gray mouse lemur (Microcebus murinus), in which females forage solitarily during the night, but form day-time sleeping groups with one to two other females. We observed 34 resident females in an 8 ha study area in Kirindy Forest, Madagascar, over three consecutive annual breeding seasons and determined genetic relationships among all members of this population. Five sleeping groups of adult females were filmed inside their roosts during one breeding season after females gave birth. The composition of groups changed substantially across years, but they always consisted of close maternal relatives. All females within a group gave birth to one to three infants. They regularly transferred only their own offspring among roosting sites, demonstrating an ability to discriminate between their own and other’s offspring, but they regularly groomed and nursed related offspring other than their own and adopted related dependent young after their mother’s death. Kin selection may therefore be the main selective force behind cooperative breeding among these closely related females with a high mortality risk, providing each of them with family insurance. 相似文献
12.
Costs and benefits associated with matings and the effects of mating frequency on fitness commonly differ between the sexes. As a result, outcrossing simultaneous hermaphrodites may prefer to copulate in the more rewarding sex role, generating conflicts over sperm donation and sperm receipt between mates. Because recent sex role preference models remain controversial, we contrast here some of their assumptions and predictions in the sea slug Chelidonura sandrana. For this hermaphrodite with sperm storage and internal fertilisation, risk-averse models assume that fitness pay-offs are constantly higher in the female than in the male function in any single mating. Moreover, excluding mutual partner assessment, these models predict male mating behaviour to be independent of receiver traits. The competing gender ratio hypothesis assumes that relative fitness pay-offs, and thus the preferred mating roles, vary and may reverse between matings and predicts that ejaculation strategies co-vary with receiver quality. We found that field mating rates of C. sandrana substantially exceeded what is required to maintain female fertility and fecundity, indicating large variation in direct female benefits between matings. We further demonstrate that male copulation duration adaptively increased with partner body size (i.e. fecundity) but decreased with recent partner promiscuity. These findings are compatible with the gender ratio hypothesis but contradict risk-averse models. 相似文献
13.
Gabriel G. González Katherina B. Brokordt Federico E. Winkler 《Marine Biology》2010,157(10):2195-2203
Several studies on individual physiological traits assume that past records may predict future performance. Marine mollusks,
as other animals, show a wide range of between- and within-individual variation of physiological traits. However, in this
group, almost nothing is known about the relative influence of genetic factors on that variation. Repeatability (R) is a measure of the consistency of the variation of a trait, which includes its genetic variance and represents the maximum
potential value of its heritability (h
2). Traits that show high inter-individual variation and high repeatability levels could potentially evolve through selection
(natural or artificial). We estimated the repeatability [using intra-class (τ) and Pearson-moment (r) correlation coefficients] of several physiological traits related to energy acquisition and allocation in juvenile Pacific
abalone Haliotis discus hannai, maintained under controlled environment growing systems. In order to estimate the range of the R values and the effect of the time elapsed between measurements on these estimates, we measured these traits monthly during
6 months for each individual. Among the physiological traits, those related to energy allocation like oxygen consumption (standard
metabolic rate, SMR) and ammonium excretion rates, and oxygen/nitrogen ratio (O/N), showed intermediate levels of repeatability
(0.48, 0.55 and 0.39, respectively), when this was estimated by τ coefficient. However, the r estimation showed that SMR and O/N repeatability were significant and high (0.6–0.7 and 0.5–0.7, respectively) during the
first 5 consecutive measurements, decreasing strongly (0.3 and 0.2, respectively) during the last measurement. For ammonia
excretion, although repeatability (r) decreased from 0.8 to 0.5 during the 6 consecutive measurements, they remain significant during the experimental period.
Therefore, our results indicate that for H. discus hannai juveniles, physiological traits like SMR, ammonia excretion and O/N are significantly repeatable (i.e. good predictors of
future measurements) during a period of 4–5 months. These significant repeatability values suggest an important genetic control
upon the phenotypic variation of these physiological traits, and could potentially respond to natural or artificial selection,
and be used in genetic improvement programs. By contrast, those traits related to energy acquisition (i.e. ingestion, absorption
and assimilation) and physiological efficiencies (i.e. net growth and scope for growth) showed very low levels of repeatability
(0–0.07). This indicates that the phenotypic variation of these traits would be more influenced by environment rather than
by genetic factors. 相似文献
14.
Fabrice Helfenstein Murielle Podevin Heinz Richner 《Behavioral ecology and sociobiology》2010,64(4):557-565
Sperm competition exerts strong selection on males to produce spermatozoa with an optimal morphology that maximizes their
fertilization success. Long sperm were first suggested to be favored because they should swim faster. However, studies that
investigated the relationship between sperm length and sperm competitive ability or sperm swimming velocity yielded contradictory
results. More recently, ratios of the different sections of a spermatozoon (the head, midpiece, and flagellum) were suggested
to be more crucial in determining swimming velocity. Additionally, sperm ability to remain and survive in the female storage
organs may also influence fertilization success, so that optimal sperm morphology may rather maximize sperm longevity than
velocity. In this study, we investigated how sperm morphology is related to sperm velocity and sperm longevity in the house
sparrow Passer domesticus. Sperm velocity was found to be correlated with head/flagellum ratio. Sperm with small heads relative to their flagellum showed
higher swimming velocity. Additionally, shorter sperm were found to live longer. Finally, we found sperm morphological traits
to vary substantially within males and the head/flagellum ratio to be unrelated to total sperm length. We discuss the hypothesis
that the substantial within-male variation in sperm morphology reflects a male strategy to produce a diversity of sperm from
long, fast-swimming to short, long-living sperm to maximize their fertilization success in a context of sperm competition. 相似文献
15.
Sexual selection theory for simultaneously hermaphroditic animals predicts an overall preference for inseminating partners
that have a relatively higher female fecundity. Previous work on the link between male mating decisions and female fecundity
has primarily focused on the effect of the partners’ body size using existing variation in this trait within a study population.
On the assumption that the body size is positively correlated with female fecundity, sperm donors should preferentially inseminate
relatively larger individuals to obtain a higher fitness gain through their male sex function. However, empirical evidence
for such size-dependent mate choice in simultaneous hermaphrodites is equivocal, possibly because of confounding variables.
We studied the mating behavior of the simultaneously hermaphroditic flatworm Macrostomum lignano and tested for a strategic mating effort in response to the feeding status of the partner. We experimentally manipulated
the feeding status of potential mating partners in order to generate variation in female fecundity among them and tested whether
this affected the copulation number and the number of sperm that the focal worm managed to store in the partner’s sperm storage
organ. We found that the manipulation of the feeding status had a strong effect on the body size of the potential mating partners
and that focal worms copulated more frequently with, and stored more sperm in well-fed partners compared to unfed partners.
Our results suggest that M. lignano adjusts its mating effort in response to the feeding status of the mating partner. 相似文献
16.
Paolo Galeotti Diego Rubolini Fabio Pupin Roberto Sacchi Mauro Fasola 《Behavioral ecology and sociobiology》2008,62(11):1739-1745
Asymmetry in traits of sexual relevance may impair copulation behaviour and sexual performance of males, ultimately resulting
in a fitness cost. Freshwater crayfish males use chelae, a sexually selected trait, to secure and position the female prior
to and during mating. Thus, a relatively large chelae asymmetry, resulting from accidental loss and regeneration of one cheliped
after autotomy, could have great consequences for male sexual behaviour. We studied copulatory behaviour and sperm expenditure
of males paired to a mated female in Austropotamobius italicus, a freshwater crayfish species where both male and female mate multiply and where last-mating males are able to actively
remove previously deposited sperm. We aimed at assessing whether male sperm removal and expenditure varied according to sperm
allocated by first-mating males, and according to copulation behaviour and phenotypic traits (carapace length, chelae length
and relative chelae asymmetry) of second-mating males. Second-mating males did not adjust their ejaculate size in relation
to first-mating male ejaculate, nor to the first-mating male’s sperm removed. Moreover, the amount of sperm removed by second-mating
males increased with increasing first-mating males ejaculate size, and first-mating male sperm remaining after removal did
not correlate with the original first-mating male ejaculate size. Interestingly, the amount of sperm removed by second-mating
males decreased with increasing relative chelae asymmetry, while increasing with male body size. However, second-mating (but
not first-mating) asymmetric-clawed males produced larger ejaculates than symmetric-clawed ones. Importantly, the proportion
of second-mating male sperm remaining after the two matings did not vary with relative chelae asymmetry nor with body size
of second-mating males. Thus, small, asymmetric-clawed crayfish males appear to adopt sperm allocation tactics that allow
them to fully compensate for their inferior sperm removal ability. 相似文献
17.
According to sexual selection theory, females should selectively mate with high-quality males to enhance offspring survival and maximize reproductive success. Yet, chimpanzee (Pan troglodytes) females are known to mate promiscuously. Although there is substantial rationale for a promiscuous mating strategy, there is also a strong expectation that females should be selective, and the question arises as to whether promiscuity precludes female choice. The aims of this study are to: (1) compare wild female chimpanzee sexual strategies throughout estrus, and (2) determine whether females exhibit mate preferences for particular males. Over 2,600 h of data were collected on two habituated chimpanzee (Pan troglodytes verus) communities in the Taï National Park, Côte dIvoire. Female mate preferences were measured by quantifying proceptivity and receptivity toward males. Results indicate that all females exhibited proceptivity and resistance to male solicitations, but that there was substantial variation in their magnitudes within and among females. Female proceptivity rates were lower and resistance rates were higher in the periovulatory period (POP) when conception is most likely. Females were more selective during POP, and more promiscuous outside of POP, suggesting that females may follow a mixed reproductive strategy, being selective when conception is likely and more promiscuous when conception is unlikely. Results from this study emphasize the importance of considering the fertility window when determining female mate preferences, and of examining female behavior in POP and non-POP phases separately when evaluating hypotheses for multi-male mating.Communicated by C. Nunn 相似文献
18.
Charlyn Partridge Ingrid Ahnesjö Charlotta Kvarnemo Kenyon B. Mobley Anders Berglund Adam G. Jones 《Behavioral ecology and sociobiology》2009,63(3):345-354
The last several decades of research in behavioral ecology have resulted in a deeper appreciation of post-mating processes
and sexual conflict in sexual selection. One of the most controversial aspects of sexual selection is cryptic mate choice.
Here, we take advantage of male pregnancy in a sex-role-reversed pipefish (Syngnathus typhle) to quantify cryptic choice based on perceived parasite load and other sources of variance in female fitness. Studies have
shown that S. typhle males preferentially mate with females with lower parasite loads and that a male’s perception of female parasite load can
be altered by tattooing females. We manipulated the apparent parasite load of females in controlled mating experiments to
test the hypothesis that post-copulatory sexual selection is dependent on a male’s perception of female parasite load in pipefish.
Our results provided no evidence for cryptic male choice based on perceived female parasite load. However, we found evidence
that eggs from larger females were more likely to result in viable offspring than eggs from smaller females and that the first
female to mate with a male transferred more eggs per copulation on average. Overall, our results show that potential for post-copulatory
sexual selection does exist in pipefish, but the male’s perception of female parasite load does not play a major role in this
process. 相似文献
19.
When two closely related species are sympatric the process of species recognition (identifying conspecifics) and mate-quality recognition (increased fitness benefits) can yield a conflict when heterospecifics resemble high-quality conspecifics. Conflict in species versus mate-quality recognition may serve as a possible mechanism for the persistence of unisexual, gynogenetic Amazon mollies (Poecilia formosa). Amazon mollies require sperm from closely related species (e.g., sailfin mollies, P. latipinna) to start embryogenesis but inheritance is strictly maternal. When choosing mates, male sailfin mollies from populations sympatric with Amazon mollies may rely on traits indicating species identity rather than those indicating mate quality. Conversely, males from allopatric populations may rely more on traits indicating mate quality. Previous work has found that male sailfin mollies in sympatry exhibit a significantly greater mating preference for female sailfin mollies over Amazon mollies compared to males in allopatry. In addition, male sailfin mollies prefer to associate with and produce more sperm in the presence of larger conspecific females, which are more fecund. We hypothesized that male sailfin mollies experience a conflict in species recognition and mate-quality recognition in the presence of Amazon mollies that are relatively larger than female sailfin mollies. To test this hypothesis, we paired males from sympatric and allopatric populations with a larger Amazon molly and a smaller female sailfin molly. We scored the number of mating attempts that males directed to conspecific and heterospecific females. Males in most sympatric and allopatric populations demonstrate no clear preference for conspecifics. In addition, we found some evidence for a difference in mating preference between allopatric and sympatric populations with males from allopatry showing a greater heterospecific mate preference. These results indicate a conflict between species and mate-quality recognition. In sympatry this conflict may contribute to the persistence of gynogenetic Amazon mollies. 相似文献
20.
A comprehensive understanding of sexual selection requires knowledge of the traits and mechanisms responsible for increasing a male’s paternity share (proportion of progeny sired) relative to that of other males mating with the same female. In this study we manipulated by starvation the expression of traits that might influence male paternity share in Tribolium castaneum. We then conducted experiments to examine how male starvation affects male performance during sequential episodes of sexual selection from mating to progeny production, and investigated female control over specific stages by using live vs dead females. Comparison of starved vs fed males revealed that T. castaneum females have control over spermatophore transfer during mating, as live females rejected inseminations by starved (“low quality”) males. None of the measured male copulatory behaviors (leg-rubbing frequency, asymmetry, and percent of time spent rubbing) affected the probability of successful insemination, but the last two were positively associated with male paternity share. Spermatophore positioning within the female reproductive tract was not affected by male treatment (starved/fed), by female treatment (live/dead), or by male copulatory behaviors. Starvation, however, had a dramatic effect on male reproductive physiology, decreasing both accessory gland size and total number of sperms transferred (but not sperm viability in seminal vesicles). In addition, females who mated to starved males stored fewer sperms in their spermathecae, which, together with decreased ejaculate size, may explain the reduced paternity share of starved males compared to fed males. This study elucidates some cryptic mechanisms influencing male reproductive success and aids our understanding of trait evolution through sexual selection. 相似文献