Data from: Divergent natural selection promotes immigrant inviability at early and late stages of evolutionary divergence

Natural selection's role in speciation has been of fundamental importance since Darwin first outlined his theory. Recently, work has focused on understanding how selection drives trait divergence, and subsequently reproductive isolation. ‘Immigrant inviability’, a barrier that arises from selection against immigrants in their non-native environment, appears to be of particular importance. Although immigrant inviability is likely ubiquitous, we know relatively little about how selection acts on traits to drive immigrant inviability, and how important immigrant inviability is at early-versus-late stages of divergence. We present a study evaluating the role of predation in the evolution of immigrant inviability in recently-diverged population pairs and a well-established species pair of Brachyrhaphis fishes. We evaluate performance in a high-predation environment by assessing survival in the presence of a predator, and swimming endurance in a low-predation environment. We find strong signatures of local adaptation and immigrant inviability of roughly the same magnitude both early and late in divergence. We find remarkably conserved selection for burst-speed swimming (important in predator evasion), and selection for increased size in low-predation environments. Our results highlight the consistency with which selection acts during speciation, and suggest that similar factors might promote initial population differentiation and maintain differentiation at late stages of divergence.自达尔文首次系统阐述其物种形成理论以来，自然选择在该过程中的作用始终是至关重要的研究主题。近年来相关研究多聚焦于解析自然选择如何推动性状分化，进而引发生殖隔离。“外来者存活劣势（Immigrant inviability）”是一类由外来个体在非原生环境中遭受选择压而形成的生殖障碍，其重要性尤为突出。尽管该劣势大概率广泛存在，但目前我们对选择如何作用于性状以催生外来者存活劣势，以及该劣势在分化早期与晚期阶段的重要性仍所知有限。本研究针对新近分化的种群对以及已稳定分化的短鳍脂鲤属（Brachyrhaphis）物种对，评估了捕食作用在其外来者存活劣势演化过程中的作用。我们通过测定捕食者存在时的个体存活率，以及低捕食压环境下的游泳耐力，来评估鱼类在高捕食压环境中的生存表现。研究发现，在分化的早期与晚期阶段，本地适应与外来者存活劣势均存在显著信号，且二者的强度大致相当。我们还发现，爆发式游泳速度（对捕食规避至关重要）以及低捕食压环境下体型增大的选择模式均极为保守。本研究结果凸显了自然选择在物种形成过程中作用模式的一致性，并表明类似的生态因子既可能推动初始种群分化，也可在分化晚期维持种群间的遗传差异。