Li Ke, Kohn Michael H, Zhang Songmei, Wan Xinrong, Shi Dazhao, Wang Deng
College of Plant Protection, China Agricultural University, 2 Yuanmingyuan West Road, Haidian District, Beijing, 100193, China.
Institute of Biosciences and Bioengineering, Rice University, 130 Anderson Biology, P.O. Box 1892, Houston, 77251-1892, USA.
BMC Evol Biol. 2017 Jun 21;17(1):145. doi: 10.1186/s12862-017-0995-y.
The colonial habit of Brandt's vole (Lasiopodomys brandtii) differs from that of most other species of the genus Microtus. The demographic history of this species and the patterns shaping its current genetic structure remain unknown. Here, we explored patterns of genetic differentiation and infered the demographic history of Brandt's vole populations through analyses of nuclear microsatellite and D-loop sequences.
Phylogenetic analyses divided the sampled populations into three main clusters, which represent the southeastern, northeastern and western parts of the total range in Mongolia and China. Molecular data revealed an ancestral area located in the southeast of the extant range, in the Xilinguole District, Inner Mongolia, China, from where Brandt's vole populations began expanding. A gene flow analysis suggested that the most likely colonization route was from the ancestral area and was followed by subsequent northeastward and westward range expansions. We identified decreases in genetic diversity with increasing distance from the founder population within the newly occupied regions (northeastern and western regions), clinal patterns in the allele frequencies, alleles that were rare in the original area that have become common in the newly occupied regions, and higher genetic differentiation in the expanded range compared with the original one.
Our results indicate that L. brandtii most likely originated from the southeastern part of its current geographic range, and subsequently colonized into the northeastern and western parts by expansion. The genetic patterns among the derived populations and with respect to the original population are consistent with that expected under genetic surfing models, which indicated that genetic drift, rather than gene flow, is the predominant factor underlying the genetic structure of expanding Brandt's vole populations.
布氏田鼠（Lasiopodomys brandtii）的集群习性与田鼠属（Microtus）的大多数其他物种不同。该物种的种群历史以及塑造其当前遗传结构的模式仍不清楚。在此，我们通过分析核微卫星和D-loop序列，探索了布氏田鼠种群的遗传分化模式并推断其种群历史。
系统发育分析将采样种群分为三个主要聚类，分别代表蒙古和中国整个分布范围的东南部、东北部和西部。分子数据显示，一个祖先区域位于现存分布范围的东南部，即中国内蒙古锡林郭勒地区，布氏田鼠种群从这里开始扩张。基因流分析表明，最可能的殖民路线是从祖先区域出发，随后是向东北和西部的范围扩张。我们发现在新占领区域（东北部和西部地区）内，遗传多样性随着与奠基种群距离的增加而降低，等位基因频率呈现渐变模式，在原区域罕见的等位基因在新占领区域变得常见，并且与原区域相比，扩张区域的遗传分化更高。
我们的结果表明，布氏田鼠很可能起源于其当前地理分布范围的东南部，随后通过扩张殖民到东北部和西部。衍生种群与原种群之间的遗传模式与遗传漂变模型预期的一致，这表明遗传漂变而非基因流是布氏田鼠种群扩张过程中遗传结构的主要影响因素。
