During range expansion, edge populations are expected to face increased genetic drift, which in turn can alter and potentially compromise adaptive dynamics, preventing the removal of deleterious mutations and slowing down adaptation. Here, we contrast populations of the European sub-species Arabidopsis lyrata ssp petraea, which expanded its Northern range after the last glaciation. We document a sharp decline in effective population size in the range-edge population and observe that non-synonymous variants segregate at higher frequencies. We detect a 4.9% excess of derived non-synonymous variants per individual in the range-edge population, suggesting an increase of the genomic burden of deleterious mutations. Inference of the fitness effects of mutations and modeling of allele frequencies under the explicit demographic history of each population predicts a depletion of rare deleterious variants in the range-edge population, but an enrichment for fixed ones, consistent with the bottleneck effect. However, the demographic history of the range-edge population predicts a small net decrease in per-individual fitness. Consistent with this prediction, the range-edge population is not impaired in its growth and survival measured in a common garden experiment. We further observe that the allelic diversity at the self-incompatibility locus, which ensures strict outcrossing and evolves under negative frequency-dependent selection, has remained unchanged. Genomic footprints indicative of selective sweeps are broader in the Northern population but not less frequent. We conclude that the outcrossing species A. lyrata ssp petraea shows a strong resilience to the effect of range expansion.

中文翻译：

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维持适应性动态并且在范围边缘异交植物群体中没有可检测到的负载

在范围扩张期间，边缘种群预计将面临更多的遗传漂变，这反过来又可能改变并可能损害适应性动态，阻止有害突变的消除并减慢适应速度。在这里，我们对比了欧洲亚种拟南芥（Arabidopsis lyrata ssp petraea）的种群，该亚种在末次冰河作用后扩大了其北部范围。我们记录了范围边缘群体中有效群体规模的急剧下降，并观察到非同义变体以更高的频率分离。我们检测到范围边缘群体中每个个体衍生的非同义变异过量 4.9%，这表明有害突变的基因组负担增加。在每个群体的明确人口统计历史下对突变的适应度效应进行推断并对等位基因频率进行建模，预测范围边缘群体中罕见有害变异的耗尽，但固定变异的富集，这与瓶颈效应一致。然而，范围边缘人口的人口统计历史预测每个个体的健康度会出现小幅净下降。与这一预测一致的是，在普通花园实验中测量的范围边缘种群的生长和生存并未受到损害。我们进一步观察到，自交不亲和基因座的等位基因多样性保持不变，这确保了严格的异交并在负频率依赖选择下进化。表明选择性清除的基因组足迹在北方人群中更广泛，但频率也同样高。我们得出的结论是，异交物种A. lyrata ssp petraea对范围扩张的影响表现出很强的恢复能力。