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Sexual selection is thought to be responsible for the rapid divergent evolution of male genitalia with several studies detecting multivariate sexual selection on genital form. However, in most cases, selection is only estimated during a single episode of selection, which provides an incomplete view of net selection on genital traits. Here, we estimate the strength and form of multivariate selection on the genitalia arch of Drosophila simulans when mating occurs in the absence of a competitor and during sperm competition, in both sperm defence and offense roles (i.e., when mating first and last). We found that the strength of sexual selection on the genital arch was strongest during noncompetitive mating and weakest during sperm offense. However, the direction of selection was similar across selection episodes with no evidence for antagonistic selection. Overall, selection was not particularly strong despite genitals clearly evolving rapidly in this species., (© 2021 The Authors. Evolution © 2021 The Society for the Study of Evolution.)

Alcohol can alter sexual behaviour. However, our understanding of alcohol's effects on sexual interactions is limited because males are usually the focus of nonhuman studies. Alcohol could in theory alter female mate-choice and, in turn, affect sexual selection, a major mechanism of evolution. Here we tested whether alcohol exposure affected female mate-preference, choosiness, and copulation duration in the fly Drosophila simulans, while simultaneously testing for genetic variation in these effects. We found that alcohol exposure did not affect copulation duration, but did weaken mate-preference, as females copulated with a broader range of males after exposure, and it tended to reduce female choosiness as females mated more quickly. Although female genotype significantly affected copulation duration and choosiness, the effects of alcohol appeared to be reasonably consistent across genotypes, but this depended on the analysis employed. Nonetheless, alcohol reduced female choosiness and weakened mate-preference, and may therefore reduce the strength of sexual selection. Testing whether these changes impact female fitness is now required. [ABSTRACT FROM AUTHOR]

The male genitals of internal fertilisers evolve rapidly and divergently, and sexual selection is generally responsible for this. Many sexually selected traits are condition‐dependent—with their expression dependent upon the resources available to be allocated to them—as revealed by genetic or environmental manipulations of condition. However, it is not clear whether male genitals are also condition‐dependent. Here we manipulate condition in two ways (via inbreeding and diet) to test the condition‐dependence of the genital arch of Drosophila simulans. We found that genital size but not genital shape suffered from inbreeding depression, whereas genital size and shape were affected by dietary manipulation of condition. The differential effects of these treatments likely reflect underlying genetic architecture that has been shaped by past selection: inbreeding depression is only expected when traits have a history of directional selection, while diet impacts traits regardless of historical selection. Nonetheless, our results suggest genitals can be condition‐dependent like other sexually selected traits. [ABSTRACT FROM AUTHOR]

Nuptial food gift provisioning by males to females at mating is a strategy in many insects that is thought to be shaped by sexual conflict or sexual selection, as it affords males access to a female's physiology. While males often attempt to use these gifts to influence female behaviour to their own advantage, females can evolve counter mechanisms. In decorated crickets, the male's nuptial gift comprises part of the spermatophore, the spermatophylax, the feeding on which deters the female from prematurely terminating sperm transfer. However, ingested compounds in the spermatophylax and attachment of the sperm‐containing ampulla could further influence female physiology and behaviour. We investigated how mating per se and these two distinct routes of potential male‐mediated manipulation influence the female transcriptomic response. We conducted an RNA sequencing experiment on gut and head tissues from females for whom nuptial food gift consumption and receipt of an ejaculation were independently manipulated. In the gut tissue, we found that females not permitted to feed during mating exhibited decreased overall gene expression, possibly caused by a reduced gut function, but this was countered by feeding on the spermatophylax or a sham gift. In the head tissue, we found only low numbers of differentially expressed genes, but a gene co‐expression network analysis revealed that ampulla attachment and spermatophylax consumption independently induce distinct gene expression patterns. This study provides evidence that spermatophylax feeding alters the female post‐mating transcriptomic response in decorated crickets, highlighting its potential to mediate sexual conflict in this system. [ABSTRACT FROM AUTHOR]

Theory shows how sexual selection can exaggerate male traits beyond naturally selected optima and also how natural selection can ultimately halt trait elaboration. Empirical evidence supports this theory, but to our knowledge, there have been no experimental evolution studies directly testing this logic, and little examination of possible associated effects on female fitness. Here we use experimental evolution of replicate populations of broad-horned flour beetles to test for effects of sex-specific predation on an exaggerated sexually selected male trait (the mandibles), while also testing for effects on female lifetime reproductive success. We find that populations subjected to male-specific predation evolve smaller sexually selected mandibles and this indirectly increases female fitness, seemingly through intersexual genetic correlations we document. Predation solely on females has no effects. Our findings support fundamental theory, but also reveal unforseen outcomes—the indirect effect on females—when natural selection targets sex-limited sexually selected characters. Natural and sexual selection can be in opposition favouring different trait sizes, but disentangling these processes empirically is difficult. Here Okada et al. show that predation on males shifts the balance of selection in experimentally evolving beetle populations, disfavoring a sexually-selected male trait but increasing female fitness. [ABSTRACT FROM AUTHOR]

Males and females share most of their genome and develop many of the same traits. However, each sex frequently has different optimal values for these shared traits, creating intralocus sexual conflict. This conflict has been observed in wild and laboratory populations of insects and affects important evolutionary processes such as sexual selection, the maintenance of genetic variation, and possibly even speciation. Given the broad impacts of intralocus conflict, accurately detecting and measuring it is important. A common way to detect intralocus sexual conflict is to calculate the intersexual genetic correlation for fitness, with negative values suggesting conflict. Here, we highlight a potential confounder of this measure—cytoplasmic incompatibility caused by the intracellular parasite Wolbachia. Infection with Wolbachia can generate negative intersexual genetic correlations for fitness in insects, suggestive of intralocus sexual conflict. This is because cytoplasmic incompatibility reduces the fitness of uninfected females mated to infected males, while uninfected males will not suffer reductions in fitness if they mate with infected females and may even be fitter than infected males. This can lead to strong negative intersexual genetic correlations for fitness, mimicking intralocus conflict. We illustrate this issue using simulations and then present Drosophila simulans data that show how reproductive incompatibilities caused by Wolbachia infection can generate signals of intralocus sexual conflict. Given that Wolbachia infection in insect populations is pervasive, but populations usually contain both infected and uninfected individuals providing scope for cytoplasmic incompatibility, this is an important consideration for sexual conflict research but one which, to date, has been largely underappreciated. Intralocus sexual conflict has been implicated in numerous evolutionary processes, and one way to detect this conflict is by calculating the intersexual genetic correlation for fitness. We demonstrate that reproductive incompatibilities caused by Wolbachia infection can mimic sexually antagonistic fitness variation and inflate signals of intralocus sexual conflict in Drosophila. [ABSTRACT FROM AUTHOR]

Aging is characterized by rising mortality, declining fertility and declines in physiological function with age (functional senescence). Sex differences in the tempo and severity of survival and fertility declines are widespread, but it is less clear how often and how much trajectories of functional senescence diverge between the sexes. We tested how physiological function changed with age in male and female elite tennis players using first-serve speed (power) and first-serve accuracy as performance measures. We found absolute differences between the sexes with men serving faster, but less accurately than women. Both power and accuracy showed senescent declines but these began earlier for power. There were signals of trait-compensation, where players with pronounced power declines showed relative increases in accuracy, which might partially buffer against power deterioration. However, there were no sex differences in how either trait changed with age, contrasting with other sports. Sex differences in functional senescence are probably shaped by interactions between natural and sexual selection, the proximate costs of trait expression and a trait's genetic architecture, and so are highly trait-specific. We discuss the strengths and potential pitfalls of using data from elite athletes to disentangle these complex interactions. [ABSTRACT FROM AUTHOR]

Variation in the strength of age-dependent natural selection shapes differences in ageing rates across species and populations. Likewise, sexual selection can promote divergent patterns of senescence across the sexes. However, the effects of these processes on the evolution of ageing have largely been considered independently, and interactions between them are poorly understood., We use experimental evolution to investigate how natural and sexual selection affect life span and ageing in Drosophila simulans., Replicate populations were evolved under lifetime monogamy (relaxed sexual selection) or lifetime polyandry (elevated sexual selection) and at one of two temperatures, 25 °C (relaxed natural selection) or 27 °C (enhanced natural selection), in a fully factorial design. We measured longevity in 150 individually housed flies taken from each of three replicate populations per selection regime., We found that natural and sexual selection affected the evolution of life span via sex-specific effects on different ageing parameters (ageing rate vs. baseline mortality): natural selection reduced the rate of ageing in both sexes but increased male baseline mortality, while sexual selection elevated baseline mortality in both sexes but particularly in males., This means that sexual and natural selection interacted to reduce male life span but acted on female life span by independently affecting particular ageing parameters. Sex-specific effects of sexual and natural selection may help explain the diverse patterns of ageing seen in nature but complicate predictions about how ageing and life span evolve across the sexes [ABSTRACT FROM AUTHOR]

Rapid and divergent evolution of male genital morphology is a conspicuous and general pattern across internally fertilizing animals. Rapid genital evolution is thought to be the result of sexual selection, and the role of natural selection in genital evolution remains controversial. However, natural and sexual selection are believed to act antagonistically on male genital form. We conducted an experimental evolution study to investigate the combined effects of natural and sexual selection on the genital-arch lobes of male Drosophila simulans. Replicate populations were forced to evolve under lifetime monogamy (relaxed sexual selection) or lifetime polyandry (elevated sexual selection) and two temperature regimes, 25°C (relaxed natural selection) or 27°C (elevated natural selection) in a fully factorial design. We found that natural and sexual selection plus their interaction caused genital evolution. Natural selection caused some aspects of genital form to evolve away from their sexually selected shape, whereas natural and sexual selection operated in the same direction for other shape components. Additionally, sexual and natural selection tended to favour larger genitals. Thus we find that the underlying selection driving genital evolution is complex, does not only involve sexual selection, and that natural selection and sexual selection do not always act antagonistically. [ABSTRACT FROM AUTHOR]

Studies investigating the genetic benefits of female mate choice frequently find Fisherian benefits to choice, at the same time as detecting small or no good genes (viability) effects. This could be because sons trade-off viability for increased mating success and, accordingly, it has been suggested that good genes benefits should be investigated in daughters. However, good genes benefits via daughters could also be disrupted by intralocus sexual conflict. As a result, it is not clear when and if good genes benefits should accrue. We investigated potential good genes effects in Drosophila simulans using an isofemale line approach. We assessed the attractiveness of males in two different ways and then measured the longevity, as well as lifetime reproductive success, of their daughters. We also assessed potential direct benefits of female mate choice and good genes effects through the longevity of sons. We found no evidence of direct or good genes benefits to females mating with attractive males, and the failure to find good genes effects via daughters was apparently not a result of masking through intralocus sexual conflict. The results obtained in the present study are consistent with previous findings in this species, and suggest that good genes benefits are at best very small in our study population. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106, 295-306. [ABSTRACT FROM AUTHOR]

Female mate choice is one mechanism of sexual selection and, provided there is adequate genetic variation in the male traits that are the target of this selection, they will evolve via female choice. Cuticular hydrocarbons (CHCs) are important in Drosophila mate choice, but relatively little is known about the underlying genetic architecture of CHC profiles in Drosophila simulans. Here, we used gas chromatography–mass spectrometry to investigate patterns of genetic variation in the CHC profiles of male and female D. simulans using isofemale lines. We found substantial genetic variation for CHC profiles and individual CHC components, and individual CHCs were frequently strongly genetically correlated, with a tendency for negative covariance between long- and short-chain CHCs in males. Intersexual genetic covariances were often weak and frequently differed in sign. These findings are novel and significant, highlighting the previously unexplored genetic architecture of CHCs in D. simulans and suggest that this architecture may facilitate sex-specific CHC evolution. [ABSTRACT FROM PUBLISHER]

The traditional view of sexual selection via female mate choice is that female preference for certain males either has no net fitness cost or is beneficial to overall female fitness. A more contemporary view is that preferred males can at times reduce female fitness. This view has arisen from the realisation that conflict between the sexes is an inevitable feature of sexual reproduction, as each sex necessarily has a different agenda for maximizing fitness. Despite the hailing of sexual conflict as a paradigm shift and its prevalence in the recent sexual selection literature, compelling evidence that attractive males reduce female fitness remains taxonomically restricted. Here we review the findings of a series of investigations into the fitness consequences of female preference in the fly Drosophila simulans and compare them with its sibling species, D. melanogaster. We show that there are stark differences in the fitness consequences of mating with preferred males in the two species and discuss this contrast with reference to the current debates in the sexual selection literature. [ABSTRACT FROM AUTHOR]

Although polyandry is common, it is often unclear why females mate with multiple males, because although polyandry may provide females with direct or indirect fitness benefits, it can also be costly. Our understanding of polyandry is also restricted by the relative paucity of studies that disentangle the fitness effects of mating more than once with a single male and mating with multiple males. Here we investigated potential benefits and costs of polyandry in the horned beetle, Gnatocerus cornutus , while controlling for the number of matings. We found that female life span was independent of mating frequency, indicating that mating itself is not very costly. However, females that mated more than once laid more eggs and had greater lifetime reproductive success than singly mated females. Because the magnitude of these effects was similar in monandrous and polyandrous females, this improved fertility was due to multiple mating itself, rather than mating with multiple males. However, although polyandrous females produced more attractive sons, these males tended to have smaller mandibles and so may fare less well in male–male competition. These results indicate that polyandry is relatively cost free, at least in the laboratory, and has direct and indirect benefits to female fitness. However, because the attractive sons produced by polyandrous females may fight less well, the indirect benefits of polyandry will depend on the intensity of male–male competition and how free females are to exert mate choice. Where competition between males is intense, polyandry benefits via son attractiveness may be reduced and perhaps even carry costs to female fitness. [ABSTRACT FROM AUTHOR]