Data from: Genome-wide set of SNPs reveals evidence for two glacial refugia and admixture from postglacial recolonization in an alpine ungulate

Past glaciation events have played a major role in shaping the genetic diversity and distribution of wild sheep in North America. The advancement of glaciers can isolate populations in ice-free refugia, where they can survive until the recession of ice sheets. The major Beringian refugium is thought to have held thinhorn sheep (Ovis dalli) populations during times of glacial advance. While isolation in the major refugium can account for much of the genetic and morphological diversity seen in extant thinhorn sheep populations, mounting evidence suggests the persistence of populations in smaller minor refugia. We investigated the refugial origins of thinhorn sheep using ~10 000 SNPs obtained via a cross-species application of the domestic sheep ovine HD BeadChip to genotype 52 thinhorn sheep and five bighorn sheep (O. canadensis) samples. Phylogenetic inference revealed a distinct lineage of thinhorn sheep inhabiting British Columbia, which is consistent with the survival of a group of thinhorn sheep in a minor refugium separate from the Beringian refugium. Isolation in separate glacial refugia probably mediated the evolution of the two thinhorn sheep subspecies, the white Dall's sheep (O. d. dalli), which persisted in Beringia, and the dark Stone's sheep (O. d. stonei), which utilized the minor refugium. We also found the first genetic evidence for admixture between sheep from different glacial refugia in south-central Yukon as a consequence of post glacial expansion and recolonization. These results show that glaciation events can have a major role in the evolution of species inhabiting previously glaciated habitats and the need to look beyond established refugia when examining the evolutionary history of such species.

冰期事件在塑造北美野生绵羊的遗传多样性与分布格局中发挥了关键作用。冰川扩张可将种群隔离于无冰避难所中，使其得以存活直至冰盖消退。主流观点认为，冰川扩张时期，白令陆桥避难所曾栖息有多尔大角羊（Ovis dalli）种群。尽管主要避难所内的种群隔离能够解释现存多尔大角羊种群中绝大多数的遗传与形态多样性，但越来越多的证据表明，小型次要避难所中也曾存在种群存续。本研究利用通过跨物种应用绵羊高密度基因芯片（ovine HD BeadChip）获得的约1万个单核苷酸多态性（Single Nucleotide Polymorphism, SNPs）位点，对52份多尔大角羊样本与5份加拿大盘羊（Ovis canadensis）样本进行基因分型，以此探究多尔大角羊的避难所起源。系统发育推断结果显示，栖息于不列颠哥伦比亚省的多尔大角羊构成一个独立演化支，这与多尔大角羊的一个类群在独立于白令陆桥避难所的次要避难所中存活的假说相符。种群在不同冰期避难所内的隔离，可能推动了两个多尔大角羊亚种的演化：一是在白令陆桥避难所存续的白色多尔大角羊（O. d. dalli），二是利用次要避难所的黑色斯通大角羊（O. d. stonei）。本研究还在育空地区中南部的绵羊种群中，首次发现了由冰期后扩张与重新定居导致的、来自不同冰期避难所的绵羊种群间遗传混合的遗传学证据。上述结果表明，冰期事件对曾栖息于冰覆生境的物种演化具有重要影响，因此在研究此类物种的演化历史时，需突破既有避难所框架的局限。