Data from: Competition for mates and the improvement of nonsexual fitness

Competition for mates can be a major source of selection, not just on secondary sexual traits but across the genome. Mate competition strengthens selection on males via sexual selection, which typically favours healthy, vigorous individuals and, thus, all genetic variants that increase overall quality. However, recent studies suggest another major effect of mate competition that could influence genome-wide selection: sexual harassment by males can drastically weaken selection on quality in females. Because of these conflicting effects, the net effect of mate competition is uncertain, though perhaps not entirely unpredictable. We propose that the environment in which mate competition occurs mediates the importance of sexual selection relative to sexual conflict, and hence the net effect of mate competition on nonsexual fitness. To test this, we performed experimental evolution with 63 fruit fly populations adapting to novel larval conditions where each population was maintained with or without mate competition. In half the populations with mate competition, adults interacted in simple, high-density environments. In the remainder, adults interacted in more spatially complex environments in which male-induced harm is reduced. Populations evolving with mate competition in the complex environment adapted faster to novel larval environments than did populations evolving without mate competition or with mate competition in the simple environment. Moreover, mate competition in the complex environment caused a substantial reduction in inbreeding depression in egg-to-adult viability relative to the other two mating treatments. These results demonstrate that the mating environment has a substantial and predictable effect on nonsexual fitness through adaptation and purging.择偶竞争不仅是驱动次级性征（secondary sexual traits）演化选择的核心因素，更是贯穿全基因组的选择压力来源。择偶竞争通过性选择（sexual selection）强化了对雄性的选择压力，而性选择通常青睐健康、强健的个体，因此会正向选择所有能提升个体整体品质的遗传变异。然而，近期研究揭示了择偶竞争的另一重要影响——该影响同样能作用于全基因组范围的选择：雄性的性骚扰（sexual harassment）会大幅削弱对雌性品质的选择压力。由于这些相互矛盾的效应，择偶竞争的净效应仍不明确，但或许并非完全不可预测。我们提出，择偶竞争发生的环境会介导性选择相对于性冲突（sexual conflict）的重要性，进而决定择偶竞争对非性适合度（nonsexual fitness）的净效应。为验证这一假说，我们以63个果蝇种群为对象开展了实验演化研究：这些种群均适应新型幼虫环境，且每个种群均在存在或不存在择偶竞争的条件下维持繁育。在半数存在择偶竞争的种群中，成虫在简单的高密度环境中进行交配互动；其余种群的成虫则在空间结构更复杂的环境中互动——此类环境可降低雄性造成的伤害。实验结果显示，在复杂环境下经历择偶竞争的种群，其对新型幼虫环境的适应速度快于无择偶竞争的种群，以及在简单环境下经历择偶竞争的种群。此外，相较于另外两种交配处理组，复杂环境下的择偶竞争显著降低了卵到成虫存活率（egg-to-adult viability）中的近交衰退（inbreeding depression）程度。本研究结果表明，交配环境可通过适应与遗传清除（purging）过程，对非性适合度产生显著且可预测的影响。