Data from: Divergent sexual selection via male competition: ecology is key

Sexual selection and ecological differences are important drivers of speciation. Much research has focused on female choice, yet the role of male competition in ecological speciation has been understudied. Here, we test how mating habitats impact sexual selection and speciation through male competition. Using limnetic and benthic species of threespine stickleback fish, we find that different mating habitats select differently on male traits through male competition. In mixed habitat with both vegetated and open areas, selection favors two trait combinations of male body size and nuptial color: large with little color and small with lots of color. This matches what we see in reproductively isolated stickleback species, suggesting male competition could promote trait divergence and reproductive isolation. In contrast, when only open habitat exists selection favors one trait combination, large with lots of color, which would hinder trait divergence and reproductive isolation. Other behavioral mechanisms in male competition that might promote divergence, such as avoiding aggression with heterospecifics, are insufficient to maintain separate species. This work highlights the importance of mating habitats in male competition for both sexual selection and speciation.

性选择（sexual selection）与生态差异是物种形成（speciation）的重要驱动因素。既往研究多聚焦于雌性配偶选择（female choice），而雄性竞争（male competition）在生态物种形成中的作用却未得到充分探讨。本研究通过雄性竞争实验，探究交配栖息地如何影响性选择与物种形成。我们以三棘刺鱼（threespine stickleback）的湖沼型（limnetic）与底栖型（benthic）物种为实验对象，发现不同交配栖息地通过雄性竞争对雄性性状产生差异化选择：在兼具植被覆盖区与开阔水域的混合栖息地中，选择倾向于两种雄性体型与婚色（nuptial color）的性状组合——体型偏大但婚色浅淡，以及体型偏小但婚色浓郁。这一结果与存在生殖隔离（reproductive isolation）的刺鱼物种所呈现的性状特征高度相符，提示雄性竞争可推动性状分化与生殖隔离的形成。与之形成对比的是，当仅存在开阔水域栖息地时，选择仅青睐单一性状组合：体型偏大且婚色浓郁，这将阻碍性状分化与生殖隔离的产生。雄性竞争中其他可能推动分化的行为机制（如避免与异种个体（heterospecifics）发生攻击行为），并不足以维持物种间的生殖隔离。本研究凸显了交配栖息地在雄性竞争中对性选择与物种形成的关键意义。