Colourful male guppies produce faster and more viable sperm

In guppies (Poecilia reticulata) precopulatory sexual selection (via female choice) and post-copulatory selection (via sperm competition) both favour males with relatively high levels of carotenoid (orange) pigmentation, suggesting that colourful males produce more competitive ejaculates. Here we test whether there is a positive association between male orange pigmentation and sperm quality. Our analysis of sperm quality focused on sperm swimming speeds (using CASA: computer-assisted sperm analysis to estimate three parameters of sperm velocity in vitro), sperm viability (proportion of live sperm per stripped ejaculate) and sperm lengths. We found that males with relatively large areas of orange pigmentation had significantly faster and more viable sperm than their less ornamented counterparts, suggesting a possible link between dietary carotenoid intake and sperm quality. By contrast, we found no relationship between sperm length (head length and total sperm length) and male phenotype. These findings, in conjunction with previous work showing that highly ornamented male guppies sire higher quality offspring, suggest that female preference for colourful males and sperm competition work in concert to favour intrinsically higher quality males.     

Cryptic female preference for colorful males in guppies

Cryptic female choice (CFC) refers to female-mediated processes occurring during or after copulation that result in biased sperm use in favor of preferred or compatible males. Despite recent empirical support for this hypothesis, evidence that CFC contributes towards the evolution of male body ornaments, in the same way that precopulatory female choice does, is currently lacking. Here, we tested the possibility that CFC selects for increased male attractiveness in the guppy Poecilia reticulata, a freshwater fish exhibiting internal fertilization. Specifically, we examined whether females are able to manipulate the number of sperm transferred or retained at copulation in favor of relatively attractive males. In support of this prediction, we found that following solicited copulations the number of sperm inseminated is influenced exclusively by the female's perception of relative male coloration, independent of any direct manipulation of males themselves. Because females prefer brightly colored males during precopulatory mate choice, our finding that colorful males are also favored as a consequence of enhanced insemination success indicates that cryptic female choice can reinforce precopulatory preferences for extravagant male ornaments.     

Conflict between direct and indirect benefits of female choice in desert Drosophila

Identifying the factors that contribute to the adaptive significance of mating preferences is one major goal of evolutionary research and is largely unresolved. Both direct and indirect benefits can contribute to mate choice evolution. Failure to consider the interaction between individual consequences of mate choice may obscure the opposing effects of individual costs and benefits. We investigate direct and indirect fitness effects of female choice in a desert fly (Drosophila mojavensis), a species where mating confers resistance to desiccation stress. Females prefer males that provide a direct benefit: greater resistance to desiccation stress. Mating preferences also appear to have indirect consequences: daughters of preferred males have lower reproductive success than daughters of unpreferred males, although additional experimentation will be needed to determine if the indirect consequences of female preferences actually arise from 'sexually antagonistic' variation. Nevertheless, the results are intriguing and are consistent with the hypothesis that an interaction between direct and indirect benefits maintains sexually antagonistic variation in these desert flies: increased desiccation resistance conferred by mating might offset the cost of producing low-fecundity daughters.     

Why do male Callosobruchus maculatus harm their mates?

Males of the bruchid beetle Callosobruchus maculatus have spineson their intromittent organs that puncture the female reproductivetract during mating. Females kick their mates during copulation.If females are prevented from kicking the males, copulationslast longer and the injuries females sustain are more severe.We tested whether or not these injuries represent real fitnesscosts that can be mitigated by kicking and also what males gainby inflicting them. Our results show that females do indeedsuffer lowered lifetime fecundity if they are prevented fromkicking. However, we could find no evidence that males gainbenefits through harming their mates. It has been suggestedthat the way females respond to the harm may benefit the malecausing it. Injured females may be less willing to remate toavoid sustaining further injuries, or they may respond by increasingtheir rate of oviposition if they perceive the injuries as athreat to their survival. In our study, however, females thatwere prevented from kicking did not respond by delaying rematingor increasing their rate of oviposition. Furthermore, preventingfemales from kicking during their second copulation did notmake their second mates more successful in sperm competition.This suggests that the spines have evolved for other reasonsthan harming the females, such as serving as an anchor duringcopulation, and that the harm they cause is a side effect ofa male adaptation and is not itself adaptive for either sex.     

Tradeoffs limit the evolution of male traits that are attractive to females

Tradeoffs occur between a variety of traits in a diversity of organisms, and these tradeoffs can have major effects on ecological and evolutionary processes. Far less is known, however, about tradeoffs between male traits that affect mate attraction than about tradeoffs between other types of traits. Previous results indicate that females of the variable field cricket, Gryllus lineaticeps, prefer male songs with higher chirp rates and longer chirp durations. In the current study, we tested the hypothesis that a tradeoff between these traits affects the evolution of male song. The two traits were negatively correlated among full-sibling families, consistent with a genetically based tradeoff, and the tradeoff was stronger when nutrients were limiting. In addition, for males from 12 populations reared in a common environment, the traits were negatively correlated within populations, the strength of the tradeoff was largely invariant across populations, and the within-population tradeoff predicted how the traits have evolved among populations. A widespread tradeoff thus affects male trait evolution. Finally, for males from four populations assayed in the field, the traits were negatively correlated within and among populations. The tradeoff is thus robust to the presence of environmental factors that might mask its effects. Together, our results indicate there is a fundamental tradeoff between male traits that: (i) limits the ability of males to produce multiple attractive traits; (ii) limits how male traits evolve; and (iii) might favour plasticity in female mating preferences.     

The young sperm gambit

Thermodynamic and oxidative damage to the condensed nuclear DNA of spermatozoa may result in age-related deterioration that results in zygote death. By definition, any such spermatozoan-age effects are direct (i.e. nonheritable) and, if they occur, females may be selected to avoid such costs. This paper examines the potential of spermatozoan-age effects to provide alternative explanations for several reproductive phenomena.     

Offspring viability benefits but no apparent costs of mating with high quality males

Traditional models of sexual selection posit that male courtship signals evolve as indicators of underlying male genetic quality. An alternative hypothesis is that sexual conflict over mating generates antagonistic coevolution between male courtship persistence and female resistance. In the scarabaeine dung beetle Onthophagus taurus, females are more likely to mate with males that have high courtship rates. Here, we examine the effects of exposing females to males with either high or low courtship rates on female lifetime productivity and offspring viability. Females exposed to males with high courtship rates mated more often and produced offspring with greater egg-adult viability. Female productivity and lifespan were unaffected by exposure to males with high courtship rates. The data are consistent with models of sexual selection based on indirect genetic benefits, and provide little evidence for sexual conflict in this system.     

Relative importance of the area and intensity of the orange spots of male guppies Poecilia reticulata as mating traits preferred by females

Digitally modified videos of male guppies Poecilia reticulata were used to examine the relative importance of the area and intensity of the orange spots as mating traits preferred by females. The females prioritized the area of the orange spots over intensity for their mate preference.     

The evolution of male genitalia: functional integration of genital sclerites in the dung beetle Onthophagus taurus

It is now widely recognized that sexual selection has been important in the rapid and divergent evolution of male genital morphology. However, distinguishing among putative mechanisms of sexual selection acting on male genital morphology represents a considerable challenge. Although there is growing evidence that variation in the size and/or shape of male genital structures can determine a male's success in gaining fertilizations, our knowledge of the functional morphology of male genitalia remains limited. Here we examine the functional morphology of genital sclerites that are known to influence paternity in the dung beetle Onthophagus taurus . We show that three of the sclerites form a functionally integrated unit that generates the tubular-shaped spermatophore and delivers its opening to the female's spermathecal duct. A fourth sclerite acts as a holdfast device during copulation. Our observations shed light on the mechanism by which these sclerites influence a male's paternity, and their patterns of phenotypic and genetic (co)variation.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 257–266.     

Selection of male traits during and after copulation in the seedbug Lygaeus simulans (Heteroptera, Lygaeidae)

In order to evaluate selection of male morphological traits during copulation, a laboratory experiment was performed with the promiscuous seedbug Lygaeus simulans. Three male traits suspected as putative targets of selection were measured: weight, fluctuating asymmetry of a measure on the forewings, and length of a conspicuous genital structure, the processus gonopori. As fitness measures we considered total fecundity (number of fertilized eggs), insemination and fertilization success (established if a female laid fertilized eggs after copulation), and the interval between copulation and oviposition. Eighty-four males were allowed a single copulation with one virgin female each. Out of 67 copulations, 27 (40.2%) resulted in fertilized eggs and the oviposition latency ranged from 6 to 26 days. Regressions of male traits on the fitness measures showed significant phenotypical selection of two male traits: (1) males of average weight are more likely to achieve fertilization and (2) the oviposition latency was shorter for males with lower asymmetry. The copulation-oviposition interval may be especially important for male fertilization success because Lygaeus males perform copulatory mate guarding and the last male copulating with a female fertilizes most of the eggs. No selection of the genitalic trait was detected.     

Male size does not affect the strength of male mate choice for high-quality females in Drosophila melanogaster

Theory predicts that the strength of male mate choice should vary depending on male quality when higher-quality males receive greater fitness benefits from being choosy. This pattern extends to differences in male body size, with larger males often having stronger pre- and post-copulatory preferences than smaller males. We sought to determine whether large males and small males differ in the strength (or direction) of their preference for large, high-fecundity females using the fruit fly, Drosophila melanogaster. We measured male courtship preferences and mating duration to show that male body size had no impact on the strength of male mate choice; all males, regardless of their size, had equally strong preferences for large females. To understand the selective pressures shaping male mate choice in males of different sizes, we also measured the fitness benefits associated with preferring large females for both large and small males. Male body size did not affect the benefits that males received: large and small males were equally successful at mating with large females, received the same direct fitness benefits from mating with large females, and showed similar competitive fertilization success with large females. These findings provide insight into why the strength of male mate choice was not affected by male body size in this system. Our study highlights the importance of evaluating the benefits and costs of male mate choice across multiple males to predict when differences in male mate choice should occur.     

Territorial male gobies respond aggressively to sneakers but do not adjust their sperm expenditure

We investigated whether mating behavior (sperm expenditure,courtship rate, and nest guarding) varied according to differentlevels of sperm competition in territorial males of two gobyspecies, the grass and the black gobies. We measured sperm expenditure(sperm released after 30 min from the beginning of the spawning),male courtship rate, and nest-guarding behavior in territorialmales of both species during simulated spawnings, in which wevaried the number of attending sneakers. Our results showedthat, in both species, territorial males adjusted their effortin nest guarding to the presence of rival sneakers by increasingthe time spent patrolling the territory and attacking the sneakers.In contrast, sperm expenditure and male courtship rate werenot influenced by the number of attending sneakers. These resultsare in agreement with those reported for other fish with alternativemating tactics and help to interpret previous inconsistenciesbetween theoretical predictions and measured levels of spermreleased at different levels of sperm competition by sneakersof the two gobiids studied here.