Department of Ecology and Evolutionary Biology, Cornell University, Corson Hall, Ithaca, NY 14853-2701, USA.
Mol Ecol. 2013 Jun;22(11):2971-85. doi: 10.1111/mec.12343. Epub 2013 May 24.
Range expansions are extremely common, but have only recently begun to attract attention in terms of their genetic consequences. As populations expand, demes at the wave front experience strong genetic drift, which is expected to reduce genetic diversity and potentially cause 'allele surfing', where alleles may become fixed over a wide geographical area even if their effects are deleterious. Previous simulation models show that range expansions can generate very strong selective gradients on dispersal, reproduction, competition and immunity. To investigate the effects of range expansion on genetic diversity and adaptation, we studied the population genomics of the bank vole (Myodes glareolus) in Ireland. The bank vole was likely introduced in the late 1920s and is expanding its range at a rate of ~2.5 km/year. Using genotyping-by-sequencing, we genotyped 281 bank voles at 5979 SNP loci. Fourteen sample sites were arranged in three transects running from the introduction site to the wave front of the expansion. We found significant declines in genetic diversity along all three transects. However, there was no evidence that sites at the wave front had accumulated more deleterious mutations. We looked for outlier loci with strong correlations between allele frequency and distance from the introduction site, where the direction of correlation was the same in all three transects. Amongst these outliers, we found significant enrichment for genic SNPs, suggesting the action of selection. Candidates for selection included several genes with immunological functions and several genes that could influence behaviour.
范围扩展极为常见，但直到最近才开始引起人们对其遗传后果的关注。随着种群的扩张，处于波前的种群经历强烈的遗传漂变，这预计会降低遗传多样性，并可能导致“等位基因冲浪”，即即使有害，等位基因也可能在广泛的地理区域内固定下来。以前的模拟模型表明，范围扩展可以在扩散、繁殖、竞争和免疫方面产生非常强烈的选择梯度。为了研究范围扩展对遗传多样性和适应性的影响，我们研究了爱尔兰银行鼩鼱（Myodes glareolus）的群体基因组学。银行鼩鼱可能是在 20 世纪 20 年代末引入的，其分布范围正在以每年约 2.5 公里的速度扩大。我们使用测序基因型分析技术，在 5979 个 SNP 位点对 281 只银行鼩鼱进行了基因分型。14 个采样点排列在三条从引入点到扩展波前的横截线上。我们发现，所有三条横截线上的遗传多样性都显著下降。然而，没有证据表明波前的位点积累了更多的有害突变。我们寻找与从引入点到距离呈强相关性的等位基因频率的异常值位点，在所有三条横截线上，相关性的方向是相同的。在这些异常值中，我们发现基因 SNP 的富集程度显著增加，这表明选择的作用。选择的候选基因包括几个具有免疫功能的基因和几个可能影响行为的基因。
