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Because of the production of males, sexual populations are expected to incur a 50% cost in potential growth rate. However, theory predicts that sexual competition between males can compensate for this cost by decreasing the mutation load of sexual populations. To test this hypothesis, I induced mutations in male bulb mites with ionizing radiation and subjected their progeny (F1) to two selective regimes differing in opportunity for sexual selection. Mutations which were not removed by selection acting on the F1 decreased embryonic viability in the F2. Viability was significantly higher in the treatment in which there was an opportunity for sexual selection than in the treatment in which sexual selection was experimentally eliminated. The results indicate that sexual selection can increase population fitness and, at least partly, compensate for the cost of sex. [ABSTRACT FROM AUTHOR]

Abstract The number of de novo mutations in the germline can be expected to increase with age in males, therefore females might decrease mutation load in their progeny by avoiding mating with older males. Here, I propose that female polyandry can be more effective in decreasing the risk of genetic disorders in progeny than pre-copulatory mate choice, particularly if sperm competitiveness declines more steeply with age than other traits affecting chances of males to mate. If faster ageing of spermatogenic tissue causes older males to transfer inadequate numbers of functional sperm, polyandry would also benefit females directly. [ABSTRACT FROM AUTHOR]

The 'good genes' hypothesis for the evolution of male secondary sexual traits poses that female preferences for such traits are driven by indirect genetic benefits. However, support for the hypothesis remains ambiguous, and, in particular, the genetic basis for the benefits has rarely been investigated. Here, we use seminatural populations of Trinidadian guppies to investigate whether sexually selected traits (orange, black and iridescent colouration, gonopodium length and body size) predict fitness measured as the number of grandoffspring, a metric that integrates across fitness components and sexes. Furthermore, we tested whether two potential sources of genetic benefits—major histocompatibility complex (MHC) genotypes and multilocus heterozygosity (MLH)—are significant predictors of fitness and of the size of sexually selected traits. We found a significant, nonlinear effect of the area of black pigmentation and male body size on the number of grandoffspring, suggesting stabilizing selection on black area, and nonlinear selection favouring small body size. MLH was heritable (h2 = 0.14) and significantly predicted the number of grandoffspring, indicating the potential for genetic benefits based on heterozygosity. We also found support for local heterozygosity effects, which may reflect a noneven distribution of genetic load across the genome. MHC genotype was not significantly associated with any tested fitness component, or with the load of Gyrodactylus parasites. Neither MHC nor MLH was significant predictor of sexually selected traits. Overall, our results highlight the role of heterozygosity in determining fitness, but do not provide support for male sexually selected traits being indicators of genetic quality. [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]