Data from: Sexual conflict and antagonistic coevolution across water strider populations

Microevolutionary studies have demonstrated sexually antagonistic selection on sexual traits, and existing evidence supports a macroevolutionary pattern of sexually antagonistic coevolution. Two current questions are how antagonistic selection within populations scales to divergence among populations, and to what extent intraspecific divergence matches species-level patterns. To address these questions, we conducted an intraspecific comparative study of sexual armaments and mating behaviours in a water strider (Gerris incognitus) in which male genitals grasp resistant females and female abdominal structures help ward off males. The degree of exaggeration of these armaments coevolves across species. We found a similar strong pattern of antagonistic coevolution among populations, suggesting that sexual conflict drives population differentiation in morphology. Furthermore, relative exaggeration in armaments was closely related to mating outcomes in a common environment. Interestingly, the effect of armaments on mating was mediated by population sexual size dimorphism. When females had a large size advantage, mating activity was low and independent of armaments, but when males had a relative size advantage, mating activity depended on which sex had relatively exaggerated armaments. Thus, a strong signal of sexually antagonistic coevolution is apparent even among populations. These results open opportunities to understand links between sexual arms races, ecological variation and reproductive isolation.

微进化研究已证实性征受到性拮抗选择（sexually antagonistic selection）的作用，现有证据亦支持性拮抗协同进化（sexually antagonistic coevolution）的宏观进化模式。当前存在两个关键科学问题：种群内的拮抗选择如何外推至种群间的分化，以及种内分化在多大程度上契合物种水平的演化模式。为解答上述问题，我们针对水黾（Gerris incognitus）开展了性军备（sexual armaments）与交配行为的种内比较研究——该物种雄性生殖器可抓握抗拒交配的雌性，雌性腹部结构可抵御雄性的侵扰。这类性军备的夸张程度在跨物种类群中呈现协同演化的格局。我们在种群间观测到了类似的强性拮抗协同进化模式，表明性冲突推动了形态学层面的种群分化。此外，性军备的相对夸张程度与共同环境下的交配结果显著相关。值得注意的是，性军备对交配过程的影响受到种群性大小二态性（sexual size dimorphism）的介导：当雌性具备体型优势时，交配活动水平较低且与性军备程度无关；而当雄性具备相对体型优势时，交配活动则取决于哪一性别的军备相对更为夸张。由此可见，即便在种群尺度下，性拮抗协同进化的显著信号亦清晰可辨。本研究结果为解析性军备竞赛、生态变异与生殖隔离（reproductive isolation）之间的内在关联提供了全新的研究契机。