The ability of populations to expand their geographical ranges, whether as invaders, agricultural strains or climate migrants, is currently one of the most serious global problems. However, fundamental mechanisms remain poorly understood regarding factors that enable certain populations, such as biological invaders, to rapidly transition to novel habitats. According to one hypothesis, environmental fluctuations in the native range could promote successful invasions by imposing balancing selection on key traits and maintaining the genetic variation that enables rapid adaptation in novel habitats. Here we test the genomic predictions of this hypothesis by performing whole-genome sequencing of multiple independent invasive freshwater and native saline populations of the copepod Eurytemora affinis complex. We found that invasive populations have repeatedly responded to selection through the parallel use of the same single-nucleotide polymorphisms and genomic loci, to a much greater degree than expected. These same loci were enriched for signatures of long-term balancing selection in the native ranges, with 15–47% of loci exhibiting significant signatures of balancing selection. The strong association between parallel evolution in the invaded range and balancing selection in the native range supports the hypothesis that fluctuating habitats can promote invasive success and that balancing selection might serve as a widespread and important mechanism that enables rapid adaptation in nature.

人口扩大其地理范围的能力，无论是作为入侵者，农业菌株还是气候移民，都是目前最严重的全球问题之一。但是，关于使某些种群（例如生物入侵者）能够迅速过渡到新的栖息地的因素的基本机制仍然知之甚少。根据一种假设，通过在关键性状上进行平衡选择并保持能够在新的生境中快速适应的遗传变异，本地范围内的环境波动可促进成功入侵。在这里，我们通过对the足类Eurytemora affinis的多个独立侵入性淡水和天然盐种群进行全基因组测序，测试了该假设的基因组预测复杂。我们发现，入侵人群通过并行使用相同的单核苷酸多态性和基因组位点反复对选择做出反应，其程度远超出预期。这些相同的基因座丰富了本地范围内长期平衡选择的特征，其中15–47％的基因座显示出平衡选择的显着特征。入侵范围内的平行进化与原生范围内的平衡选择之间的密切联系支持以下假设：动荡的栖息地可以促进入侵成功，而平衡选择可能是广泛而重要的机制，可以使自然快速适应。