Despite the homogenizing effect of strong gene flow between two populations, adaptation under symmetric divergent selection pressures results in partial reproductive isolation: adaptive substitutions act as local barriers to gene flow, and if divergent selection continues unimpeded, this will result in complete reproductive isolation of the two populations, i.e. speciation. However, a key issue in framing the process of speciation as a tension between local adaptation and the homogenizing force of gene flow is that the mutation process is blind to changes in the environment and therefore tends to limit adaptation. Here we investigate how globally beneficial mutations (GBMs) affect divergent local adaptation and reproductive isolation. When phenotypic divergence is finite, we show that the presence of GBMs limits local adaptation, generating a persistent genetic load at the loci that contribute to the trait under divergent selection and reducing genome-wide divergence. Furthermore, we show that while GBMs cannot prohibit the process of continuous differentiation, they induce a substantial delay in the genome-wide shutdown of gene flow.

This article is part of the theme issue ‘Towards the completion of speciation: the evolution of reproductive isolation beyond the first barriers’.

尽管两个种群之间强大的基因流动具有均质效应，但在对称的发散选择压力下的适应仍会导致部分生殖隔离：适应性替代会成为基因流动的局部障碍，并且如果发散选择继续不受阻碍，这将导致该种群的完全生殖隔离。两个种群，即物种形成。但是，将物种形成过程构架为局部适应和基因流均化力之间的张力的一个关键问题是突变过程对环境的变化视而不见，因此倾向于限制适应。在这里，我们调查了全球有益突变（GBMs）如何影响不同的局部适应和生殖隔离。当表型差异是有限的时，我们表明GBM的存在限制了局部适应，在基因座处产生持久的遗传负荷，有助于在选择差异下降低性状，并降低全基因组的差异。此外，我们表明，尽管GBM不能禁止持续分化的过程，但它们会导致基因组范围的基因流关闭显着延迟。

本文是主题“走向物种形成：生殖隔离超越第一个障碍的演变”的一部分。