Genomic time-series data show that gene flow maintains high genetic diversity despite substantial genetic drift in a butterfly species

Effective population size affects the efficacy of selection, rate of evolution by drift, and neutral diversity levels. When species are subdivided into multiple populations connected by gene flow, evolutionary processes can depend on global or local effective population sizes. Theory predicts that high levels of diversity might be maintained by gene flow, even very low levels of gene flow, consistent with species long-term effective population size, but tests of this idea are mostly lacking. Here, we show that Lycaeides butterfly populations maintain low contemporary (variance) effective population sizes (e.g., ~200 individuals) and thus evolve rapidly by genetic drift. In contrast, populations harbored high levels of genetic diversity consistent with an effective population size several orders of magnitude larger. We hypothesized that the differences in the magnitude and variability of contemporary versus long-term effective population sizes were caused by gene flow of sufficient magni...有效种群大小（effective population size）会影响选择效率、遗传漂变（genetic drift）驱动的进化速率，以及中性多样性水平。当物种被划分为多个通过基因流（gene flow）相连的种群时，进化过程的特征可能取决于全局或局域有效种群大小。现有理论预测，基因流可维持高水平的遗传多样性——即便仅存在极低水平的基因流，也能维持与物种种群长期有效大小相符的多样性水平，但目前针对该假说的验证工作大多仍未开展。 本研究表明，莱卡蝶属（Lycaeides）蝴蝶的种群维持着较低的当代（方差）有效种群大小（例如约200个个体），因此会通过遗传漂变快速演化。与之形成鲜明对比的是，这些种群却维持着高水平的遗传多样性，这与大数个数量级的有效种群大小相符。我们提出假说：当代与长期有效种群大小在量级与波动性上的差异，由足够强度的基因流所致……