Data from: Evolution of pre-mating reproductive isolation among conspecific populations of the sea rock-pool beetle Ochthebius urbanelliae driven by reinforcing natural selection

How natural selection might be involved in speciation remains a fundamental question in evolutionary biology. When two or more species co-occur in the same areas, natural selection may favour divergence in mating traits. By acting in sympatric but not allopatric populations, natural selection can also affect mate choice within species and ultimately initiate speciation among conspecific populations. Here we address this potential effect in the sea rock-pool beetles Ochthebius quadricollis and O.urbanelliae. The two species, which inhabit the Mediterranean coasts, co-occurr syntopically in an area along the Italian Tyrrhenian coast and completed reproductive isolation by reinforcement. In this paper, through mating trials under laboratory conditions between conspecific populations, we found in O.quadricollis no deviations from random mating. Conversely, in O.urbanelliae, we found a clear pattern of pre-mating isolation between the reinforced populations sympatric with O.quadricollis and those non-reinforced allopatric. This pattern is consistent with the view that natural selection, which completed the reproductive isolation between the two species in sympatry, led incidentally also to partial pre-mating reproductive isolation (IPSI estimator from 0.683 to 0.792) between conspecific populations of O.urbanelliae. This case study supports an until recently underappreciated role of natural selection resulting from species interactions in initiating speciation.

自然选择如何参与物种形成过程，始终是进化生物学领域的核心基础性问题。当两个或多个物种同域（sympatric）分布时，自然选择可能会推动其交配相关性状发生分化。若自然选择仅作用于同域种群而非异域（allopatric）种群，同样可以影响物种内部的配偶选择，最终启动同种种群间的物种形成过程。本研究以海岩池甲虫*Ochthebius quadricollis*与*Ochthebius urbanelliae*为研究对象，探究这一潜在效应。这两个物种均栖息于地中海沿岸，在意大利第勒尼安海沿岸的一片区域内实现了同域同生境共存，并通过生殖强化（reinforcement）完成了生殖隔离。本研究通过实验室条件下同种种群间的交配实验发现，*O. quadricollis*未出现偏离随机交配的现象；与之相反，*O. urbanelliae*则呈现出清晰的交配前生殖隔离模式：与其发生同域分布并经生殖强化完成隔离的种群，与未经历强化作用的异域种群之间存在显著分化。这一结果与下述观点一致：在同域分布环境中促成两物种间生殖隔离的自然选择，意外地也引发了*O. urbanelliae*同种种群间的部分交配前生殖隔离（交配前生殖隔离指数IPSI estimator，取值范围为0.683至0.792）。本案例研究证实了物种间相互作用所产生的自然选择在启动物种形成过程中此前未被充分重视的作用。