Data from: Long-distance dispersal suppresses introgression of local alleles during range expansions

During range expansions, even low levels of interbreeding can lead to massive introgression of local alleles into an invader's genome. Nonetheless, this pattern is not always observed in human populations. For instance, European Americans in North America are barely introgressed by Amerindian genes in spite of known contact and admixture. With coalescent spatially explicit simulations, we examined the impact of long-distance dispersal (LDD) events on introgression of local alleles into the invading population using a set of different demographic scenarios applicable to a diverse range of natural populations and species. More specifically, we consider two distinct LDD models: one where LDD events originate in the range core and targets only the expansion front and a second one where LDD events can occur from any area to any other. We find that LDD generally prevents introgression, but that LDD events specifically targeting the expansion front are most efficient in suppressing introgression. This is likely due to the fact that LDD allows for the presence of a larger number of invader alleles at the wave front, where effective population size is thus increased and local introgressed alleles are rapidly outnumbered. We postulate that the documented settlement of pioneers directly on the wave front in North America has contributed to low levels of Amerindian admixture observed in European Americans and that this phenomenon may well explain the lack of introgression after a range expansion in natural populations without the need to evoke other mechanisms such as natural selection.

在种群范围扩张过程中，即便仅发生低水平的跨群杂交，也可能引发本地等位基因大量渐渗进入入侵种群的基因组。但这一规律在人类群体中并非普遍成立。例如，北美欧洲裔人群虽与美洲原住民存在已知的接触与基因混血，却几乎未受到美洲原住民基因的渐渗。本研究采用空间显式溯祖模拟（spatially explicit coalescent simulations），针对适配多类自然种群与物种的多样化种群动态情景，探究了长距离扩散（long-distance dispersal, LDD）事件对本地等位基因渐渗进入入侵种群的作用效应。具体而言，我们考量了两类差异化的LDD模型：一类的LDD事件起源于种群分布核心区，且仅靶向扩张波锋；另一类则允许LDD事件从任意区域发生至其他任意区域。研究结果显示，LDD总体上会抑制基因渐渗，而专门靶向扩张波锋的LDD事件在抑制渐渗方面效果最为显著。这一现象的潜在机制为：LDD使得扩张波锋处存在更多的入侵种群等位基因，进而提升了该区域的有效种群大小，使本地渐渗等位基因迅速被稀释并占据少数。我们据此推测，北美地区开拓者直接定居于扩张波锋的已记载案例，或是导致欧洲裔美国人美洲原住民混血水平较低的重要原因；且该现象或可解释自然种群在范围扩张后未出现显著基因渐渗的现象，无需借助自然选择等其他演化机制。