Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, UK.
Department of Marine Sciences, Centre for Marine Evolutionary Biology, University of Gothenburg, Gothenburg, Sweden.
Philos Trans R Soc Lond B Biol Sci. 2020 Aug 31;375(1806):20190531. doi: 10.1098/rstb.2019.0531. Epub 2020 Jul 13.
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具有同质化效应，但在对称的发散选择压力下的适应会导致部分生殖隔离：适应性替代作为基因流动的局部障碍，如果发散选择不受阻碍地继续下去，这将导致两个种群的完全生殖隔离，即物种形成。然而，将物种形成过程表述为局部适应和基因流同质化力量之间的紧张关系的一个关键问题是，突变过程对环境变化是盲目的，因此往往会限制适应。在这里，我们研究了全局有益突变 (GBMs) 如何影响发散的局部适应和生殖隔离。当表型分歧是有限的时，我们表明，GBMs 的存在限制了局部适应，在对发散选择起作用的性状的位点上产生了持续的遗传负荷，并降低了全基因组的分歧。此外，我们表明，虽然 GBMs 不能阻止连续分化的过程，但它们会导致全基因组基因流动中断的过程大大延迟。本文是主题为“迈向物种形成的完成：生殖隔离在第一道障碍之外的进化”的一部分。
