Data from: Sexual selection is ineffectual or inhibits the purging of deleterious mutations in Drosophila melanogaster

The effects of sexual selection on population mean fitness are unclear and a subject of debate. Recent models propose that, because reproductive success may be condition-dependent, much of the genome may be a target of sexual selection. Under this scenario, mutations that reduce health, and thus non-sexual fitness, may also be deleterious with respect to reproductive success, meaning that sexual selection may contribute to the purging of deleterious alleles. We tested this hypothesis directly by subjecting replicate Drosophila melanogaster populations to two treatments that altered the opportunity for sexual selection and then tracked changes in the frequency of six separate deleterious alleles with recessive and visible phenotypic effects. While natural selection acted to decrease the frequency of all six mutations, the addition of sexual selection did not aid in the purging of any of them, and for three of them appears to have hampered it. Courtship and mating have harmful effects in this species and mate choice assays showed that males directed more courtship and mating behavior towards wild-type over mutant females, providing a likely explanation for sexual selection’s cost. Whether this cost extends to other mutations (e.g., those lacking visible phenotypic effects) is an important topic for future research.性选择对种群平均适合度的影响尚无定论，且始终是学界争论的焦点议题。近期相关模型指出，由于繁殖成功率可能存在条件依赖性，基因组的绝大多数区域或许均可作为性选择的作用靶点。在此情境下，那些降低个体健康水平、进而降低非性适合度的突变，对繁殖成功率而言同样可能具有有害性，这意味着性选择或许有助于清除有害等位基因（deleterious alleles）。我们通过将重复构建的黑腹果蝇（Drosophila melanogaster）种群划分为两种处理组以改变其性选择发生机会，并后续追踪了六个独立的、具有隐性且可见表型效应的有害等位基因的频率变化，直接验证了这一假说。尽管自然选择能够降低全部六种突变的频率，但额外引入的性选择并未对任何一种突变的清除起到促进作用，甚至对其中三种突变的清除产生了阻碍效果。该物种的求偶与交配行为会产生有害影响，配偶选择实验结果表明，雄性会向野生型雌性投入更多的求偶与交配行为，而非突变型雌性，这或可解释性选择的代价。这种代价是否会延伸至其他突变（例如那些不具有可见表型效应的突变），是未来研究的重要课题。