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.

雄性生殖器形态通过交配后性选择演化，是学界广泛认可的观点。与之相对，针对生殖器演化的交配前性选择假说却未受到足够关注。本研究针对阿娜果蝇（Drosophila ananassae）的雄性生殖器棘突可提升雄性交配竞争成功率这一假说展开验证。本研究利用激光手术操控该性状的大小，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而完全无法交配；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%。相较于非竞争环境，在性竞争环境中，棘突长度缩短所导致的交配成功率下降幅度显著更高；且雌性对不同处理组的雄性均表现出相似的抵抗行为，这直接证明了生殖器棘突在提升交配竞争成功率中的作用。鉴于这类棘突在果蝇属中广泛分布，且动物界中其他具备交配前功能的生殖器性状也普遍存在，因此交配前性选择对生殖器演化的影响可能比此前认知的更为广泛深远。