Data from: Constrained evolution of the sex comb in Drosophila simulans

Male fitness is dependent on sexual traits that influence mate acquisition (pre-copulatory sexual selection) and paternity (post-copulatory sexual selection), and while many studies have documented the form of selection in one or the other of these arenas, fewer have done it for both. Nonetheless, it appears that the dominant form of sexual selection is directional, although theoretically, populations should converge on peaks in the fitness surface, where selection is stabilizing. Many factors, however, can prevent populations from reaching adaptive peaks. Genetic constraints can be important if they prevent the development of highest fitness phenotypes, as can the direction of selection if it reverses across episodes of selection. In this study, we examine the evidence that these processes influence the evolution of the multivariate sex comb morphology of male Drosophila simulans. To do this, we conduct a quantitative genetic study together with a multivariate selection analysis to infer how the genetic architecture and selection interact. We find abundant genetic variance and covariance in elements of the sex comb. However, there was little evidence for directional selection in either arena. Significant nonlinear selection was detected prior to copulation when males were mated to non-virgin females, and post-copulation during sperm offence (again with males mated to non-virgins). Thus contrary to our predictions, the evolution of the D. simulans sex comb is limited neither by genetic constraints nor by antagonistic selection between pre- and post-copulatory arenas, but nonlinear selection on the multivariate phenotype may prevent sex combs from evolving to reach some fitness maximising optima.雄性适合度依赖于影响配偶获取（交配前性选择，pre-copulatory sexual selection）与父权获得（交配后性选择，post-copulatory sexual selection）的性征。尽管诸多研究已在其中一类选择场景中阐明了选择的作用形式，但同时针对两类场景开展相关研究的报道则相对较少。尽管如此，现有证据表明性选择的主流形式为定向选择（directional selection）；但从理论层面而言，种群应收敛至适合度曲面（fitness surface）的峰值处，此时选择为稳定选择（stabilizing selection）。然而诸多因素会阻碍种群抵达适应峰值（adaptive peak）：若遗传限制（genetic constraint）阻碍了高适合度表型的演化，则遗传限制可发挥重要作用；若不同选择阶段的选择方向发生逆转，亦会产生类似影响。本研究旨在探究上述过程如何影响雄性模拟果蝇（Drosophila simulans）性梳的多变量形态演化。为此，我们结合定量遗传学研究（quantitative genetic study）与多变量选择分析（multivariate selection analysis），以推断遗传架构与选择的相互作用模式。我们在性梳的组成结构中发现了丰富的遗传方差（genetic variance）与协方差（covariance）。但两类选择场景中均未发现显著的定向选择证据。当雄性与非处女雌蝇交配时，我们在交配前阶段检测到了显著的非线性选择（nonlinear selection）；在交配后精子竞争进攻阶段（sperm offence，同样使用与非处女雌蝇交配的雄性）亦检测到了此类选择。因此与我们的预测相悖，模拟果蝇性梳的演化既未受遗传限制的约束，也未受交配前与交配后场景间拮抗选择（antagonistic selection）的制约；但针对多变量表型的非线性选择，或会阻碍性梳演化至部分适合度最适值（fitness maximising optima）。