Data from: The precopulatory function of male genital spines in Drosophila ananassae [Doleschall] (Diptera: Drosophilidae) revealed by laser surgery

That male genital morphology evolves via postcopulatory sexual selection is a widely held view. In contrast, the pre-copulatory sexual selection hypothesis for genital evolution has received less attention. Here, we test the hypothesis that male genital spines of Drosophila ananassae promote competitive male copulation success. Using laser surgery to manipulate trait size, we demonstrate that incremental reductions of spine length progressively reduce male copulation success: males without spines failed entirely to copulate because of an inability to couple the genitalia together, whereas males with halfway ablated and blunted spines suffered reductions in copulation success of 87% and 13%, respectively. The decrease in copulation success resulting from spine length reduction was markedly stronger in sexually competitive environments than in non-competitive environments, and females expressed resistance behaviors similarly toward competing male treatments, demonstrating directly the role of genital spines in promoting competitive copulation success. Because these spines are widespread within Drosophila, as are other genital traits with pre-copulatory functions among animals, pre-copulatory sexual selection may have a more pervasive role in genital evolution than previously recognized.

雄性生殖器形态经由交配后性选择（postcopulatory sexual selection）演化，是目前被广泛接受的学术观点。与之相对，针对生殖器演化的交配前性选择（pre-copulatory sexual selection）假说则较少受到关注。本研究旨在验证以下假说：拟暗果蝇（Drosophila ananassae）的雄性生殖器棘突，可提升雄性在交配竞争中的成功率。本研究通过激光手术操控该性状的尺寸，结果显示棘突长度的逐步缩短会持续降低雄性的交配成功率：无棘突的雄性因无法完成生殖器对接，完全丧失交配能力；而半切除棘突与棘突钝化的雄性，其交配成功率分别下降了87%与13%。在交配竞争环境中，棘突长度缩短导致的交配成功率下降幅度显著高于非竞争环境；且雌性对各竞争雄性处理组均表现出相似的抗拒行为，这直接证明了生殖器棘突在提升雄性交配竞争成功率中的作用。鉴于这类棘突在果蝇属中广泛存在，且动物界中其他具备交配前功能的生殖器性状也普遍分布，因此交配前性选择在生殖器演化中所扮演的角色，或许比此前学界认知的更为广泛。