Parallel loss of function at major flowering time loci underlie adaptive rescue in colonising Arabidopsis lineages. CVI_ADAPT

During environmental change, small populations confront high extinction risk due to limited genetic variation and reduced efficiency of selection. Here, we reconstruct the colonisation and adaptive history of Arabidopsis populations from the Cape Verde Islands, which lie at the edge of the species distribution, to examine how populations adapt to sudden and extreme environmental change. Cape Verde populations migrated via long-range dispersal from the Moroccan Atlas mountains resulting in an immediate shift to a climate defined by a short growing season and limited, highly variable rainfall. We find that adaptation occurred via parallel reduction in flowering time across islands and that this shift to early flowering was mediated largely by three large-effect variants: a loss of function in FLC on one island and of FRI in the other. Evolutionary reconstructions reveal that these variants appeared early in the history of island populations and rapidly rose in frequency, consistent with a role in rescue from extinction. Our results reveal a central role for new large effect variants in the evolutionary rescue of fragile small populations during environmental change scenarios.

在环境变化过程中，小型种群因遗传变异有限、自然选择效率下降而面临极高的灭绝风险。本研究对位于物种分布边缘的佛得角群岛拟南芥（Arabidopsis）种群的定殖与适应历史进行重建，以探究种群如何适应突发且极端的环境变化。佛得角群岛的种群通过长距离扩散从摩洛哥阿特拉斯山脉迁徙而来，随即面临生长季短促、降雨有限且波动剧烈的气候环境。我们发现，各岛屿的开花时间均呈现平行缩短的适应性演化，且这一早开花转变主要由三个大效应变异介导：其中一个岛屿上的FLC（FLOWERING LOCUS C）功能丧失变异，以及另一个岛屿上的FRI（FRIGIDA）功能丧失变异。演化重建结果显示，这些变异在岛屿种群历史早期便已出现，并迅速在种群中频率升高，这与它们在拯救种群免于灭绝中发挥的作用一致。我们的研究结果揭示了新的大效应变异在环境变化场景下对脆弱小型种群进化拯救的核心作用。