Data from: Sexual selection on spontaneous mutations strengthens the between-sex genetic correlation for fitness

A proposed benefit to sexual selection is that it promotes purging of deleterious mutations from populations. For this benefit to be realised, sexual selection, which is usually stronger on males, must purge mutations deleterious to both sexes. Here, we experimentally test the hypothesis that sexual selection on males purges deleterious mutations that affect both male and female fitness. We measured male and female fitness in two panels of spontaneous mutation-accumulation lines of the fly, Drosophila serrata, each established from a common ancestor. One panel of mutation accumulation lines limited both natural and sexual selection (LS lines), whereas the other panel limited natural selection, but allowed sexual selection to operate (SS lines). Although mutation accumulation caused a significant reduction in male and female fitness in both the LS and SS lines, sexual selection had no detectable effect on the extent of the fitness reduction. Similarly, despite evidence of mutational variance for fitness in males and females of both treatments, sexual selection had no significant impact on the amount of mutational genetic variance for fitness. However, sexual selection did reshape the between-sex correlation for fitness: significantly strengthening it in the SS lines. After 25 generations, the between-sex correlation for fitness was positive but considerably less than one in the LS lines, suggesting that, although most mutations had sexually concordant fitness effects, sex-limited and/or sex-biased mutations contributed substantially to the mutational variance. In the SS lines this correlation was strong and could not be distinguished from unity. Individual-based simulations that mimick the experimental setup reveal two conditions that may drive our results: (1) a modest-to-large fraction of mutations have sex-limited (or highly sex-biased) fitness effects, and (2) the average fitness effect of sex-limited mutations is larger than the average fitness effect of mutations that affect both sexes similarly.

性选择（sexual selection）的一项已被提出的益处在于，它可促进种群中有害突变（deleterious mutations）的清除。要实现这一益处，通常对雄性作用更强的性选择，必须能够清除对两性均有害的突变。本研究通过实验验证了如下假说：作用于雄性的性选择能够清除同时影响雄性与雌性适合度（fitness）的有害突变。
我们以源自同一共同祖先的锯缘果蝇（Drosophila serrata）自发突变积累系（mutation-accumulation lines）的两个组群为材料，测定了其雌雄个体的适合度。其中一组突变积累系同时限制了自然选择（natural selection）与性选择（以下简称LS系），另一组则仅限制自然选择，保留性选择的作用（以下简称SS系）。
尽管在LS系与SS系中，突变积累均导致雌雄适合度出现显著下降，但性选择对适合度下降的幅度并无可检测到的影响。类似地，尽管两种处理组的雌雄个体均存在适合度的突变方差，但性选择对适合度的突变遗传方差总量并无显著影响。
但性选择确实重塑了适合度的两性间相关性：在SS系中显著增强了该相关性。经过25代培养后，LS系中适合度的两性间相关性为正，但显著小于1，这表明尽管多数突变的适合度效应在两性间一致，但性别限制性突变和/或性别偏倚突变对突变方差的贡献较大。而在SS系中，该相关性极强，无法与1（即完全正相关）区分开来。
基于个体的模拟实验（模拟本实验设置）揭示了两个可解释本研究结果的条件：其一，相当比例的突变具有性别限制性（或高度性别偏倚）的适合度效应；其二，性别限制性突变的平均适合度效应，大于对两性影响相近的突变的平均适合度效应。