Sexual selection accelerates the elimination of a deleterious mutant in Drosophila melanogaster

Although theory indicates that indirect genetic benefits through mate choice should be widespread, empirical work has often either failed to detect the operation of such benefits or shown a net cost to the presence of sexual selection. We tested whether sexual selection can increase the speed with which a conditionally deleterious allele is removed from a laboratory population of Drosophila melanogaster. The alcohol dehydrogenase null allele (Adh-) confers slightly lower viability than wild-type alleles in the absence of ethanol but is lethal in homozygotes when ethanol comprises 6% of the medium. We tracked the frequency of this allele in artificially constructed populations reared at three different levels of ethanol (0%, 2%, and 4%) that either experienced sexual selection or did not. Loss of the deleterious Adh- allele was more rapid when sexual selection was allowed to act, especially in the presence of ethanol. We also quantified the strength of both nonsexual and sexual selection against the Adh- allele using maximum-likelihood estimation. In contrast to recent experiments employing monogamy/polygamy designs, our results demonstrate a fitness benefit to sexual selection. This is consistent with the operation of good-genes female choice.