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（speciation），始终是进化生物学（evolutionary biology）中的核心科学问题。当两个或多个物种在同一区域共存时，自然选择可能会推动交配性状的分化。自然选择可作用于同域（sympatric）种群而非异域（allopatric）种群，进而影响物种内部的配偶选择，并最终启动同种（conspecific）种群间的物种形成过程。本研究以海潮池甲虫（sea rock-pool beetles）Ochthebius quadricollis与O.urbanelliae为研究对象，探讨自然选择的这一潜在效应。这两个栖息于地中海沿岸的物种，在意大利第勒尼安海岸的一处区域实现了同生境（syntopic）共存，并通过强化作用（reinforcement）完成了生殖隔离（reproductive isolation）。本文通过实验室条件下的同种（conspecific）种群交配实验（mating trials）发现，O.quadricollis未出现偏离随机交配的情况。与之相反，O.urbanelliae则呈现出清晰的交配前生殖隔离（pre-mating isolation）模式：与其同域且已完成生殖强化的种群，与非强化的异域（allopatric）种群之间存在显著的交配前隔离。该模式支持如下观点：在同域（sympatric）环境中促成两个物种间生殖隔离的自然选择，无意间也导致了O.urbanelliae同种（conspecific）种群间出现了部分交配前生殖隔离——其IPSI指数（IPSI estimator）取值范围为0.683至0.792。本案例研究证实，物种间相互作用产生的自然选择，在启动物种形成过程中具有此前未被充分重视的作用。