晚第四纪环境变化对蒙古国长尾黄鼠分化的影响
Impacts of late Quaternary environmental change on the long-tailed ground squirrel (Urocitellus undulatus) in Mongolia
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摘要: 迄今为止关于第四纪冰期如何影响亚洲内陆动植物的研究几乎空白，而研究的作者测定了蒙古国境内128个体长尾黄鼠的线粒体基因，首次通过分子系统学的方法对该地区的哺乳动物地理分化和种群动态进行了系统研究。结果显示蒙古国内的长尾黄鼠分为两个显著分化的遗传支系，对应于指名亚种和阿尔泰亚种；其中阿尔泰亚种广泛分布于蒙古国中西部的大部分地区，形成五个独立的线粒体进化枝，但进化枝之间的遗传差异较小，且相互之间的亲缘关系无法得到解决，暗示进化支系是在近期的快速分化中形成的。系统地理结构分析也支持阿尔泰亚种的地理格局符合依赖距离隔离的分化模型。 遗传多样性分析则显示阿尔泰亚种的遗传多态性较高，且经历了种群扩张。基于上述结果，作者认为蒙古国的的长尾黄鼠阿尔泰亚种的地理遗传分化模式是第四纪环境变化导致种群扩散和隔离分化的结果：冰期中，长尾黄鼠向低海拔地区迁移，并通过低矮的丘陵地区进行长距离扩散；当冰期结束之后，长尾黄鼠重新回到中高海拔山地，并在之后的干旱化中形成较为明显的地理遗传结构。Abstract: Impacts of Quaternary environmental changes on mammal faunas of central Asia remain poorly understood due to a lack of geographically comprehensive phylogeographic sampling for most species. To help address this knowledge gap, we conducted the most extensive molecular analysis to date of the long-tailed ground squirrel (Urocitellus undulatus Pallas 1778) in Mongolia, a country that comprises the southern core of this species’ range. Drawing on material from recent collaborative field expeditions, we genotyped 128 individuals at 2 mitochondrial genes (cytochrome b and cytochrome oxidase I; 1 797 bp total). Phylogenetic inference supports the existence of two deeply divergent infraspecific lineages (corresponding to subspecies U. u. undulatus and U. u. eversmanni), a result in agreement with previous molecular investigations but discordant with patterns of range-wide craniometric and external phenotypic variation. In the widespread western eversmanni lineage, we recovered geographically-associated clades from the: (a) Khangai, (b) Mongolian Altai, and (c) Govi Altai mountain ranges. Phylogeographic structure in U. u. eversmanni is consistent with an isolation-by-distance model; however, genetic distances are significantly lower than among subspecies, and intra-clade relationships are largely unresolved. The latter patterns, as well as the relatively higher nucleotide polymorphism of populations from the Great Lakes Depression of northwestern Mongolia, suggest a history of range shifts into these lowland areas in response to Pleistocene glaciation and environmental change, followed by upslope movements and mitochondrial lineage sorting with Holocene aridification. Our study illuminates possible historical mechanisms responsible for U. undulatus genetic structure and contributes to a framework for ongoing exploration of mammalian response to past and present climate change in central Asia.
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