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物种形成理论以来，自然选择在物种形成过程中的核心地位始终毋庸置疑。近期相关研究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。其中，“移民不可存活性（Immigrant inviability）”——即外来个体在非原生环境中遭遇选择压力而形成的生殖隔离屏障——其重要性尤为突出。尽管移民不可存活性可能广泛存在于各类类群中，但目前学界对自然选择如何作用于性状以催生该屏障，以及其在物种分化早期与晚期阶段的相对重要性仍知之甚少。本研究针对近期分化的种群对以及分化成熟的短颌脂鲤属（Brachyrhaphis）物种对，探讨捕食压力在移民不可存活性演化中的作用。我们通过测定捕食者存在条件下的个体存活率，评估高捕食压力环境中的生存表现；同时通过测定游泳耐力，评估低捕食压力环境中的个体性能。研究结果显示，在物种分化的早期与晚期阶段，局部适应与移民不可存活性的信号强度均处于相近水平。我们还发现，针对逃逸捕食所需的爆发游泳速度的选择压力高度保守，而在低捕食压力环境中，个体体型增大的选择优势同样显著。本研究结果凸显了自然选择在物种形成过程中的作用一致性，并表明类似的选择压力既可能推动种群初始分化，也可在分化晚期维持种群间的遗传差异。