长爪沙鼠线粒体细胞色素b基因的遗传变异及地理分化

本文基于6个种群52个个体的线粒体细胞色素b（Cyt b）基因全序列的遗传变异分析,探讨了我国长爪沙鼠种群的遗传结构和种群历史。在1140bp Cyt b基因的碱基序列中,共发现了74个变异位点,其中转换和颠换位点分别为65和9个,共定义了37个单倍型。种群差异分析表明包头种群与其他种群之间都存在着显著的遗传差异,而其他种群间遗传差异则不显著。52个个体在系统发生树中明显聚为两支（Clade A和Clade B）,其中Clade B仅含有贺兰山东部种群中的3种单倍型,而其余的单倍型分布于Clade A中。来自CladeA的49个个体的歧点分布分析结果呈单峰状,提示长爪沙鼠种群可能在历史上经历了种群增长和扩张事件,这一结果同时也得到了Tajima检验结果（D=-1.86,P〈0.05）和Fu检验结果（Fs=-21.89,P〈0.05）的支持。通过种群扩张系数（τ）和分子钟的推算提示该种群扩张事件大约发生于11万年前。我们的研究结果表明,长爪沙鼠在第四纪冰期中形成了明显的隔离分化,而贺兰山东部可能作为冰期避难所,包含于所有的谱系分支中,在末次间冰期种群进行了强烈的扩张,从而形成当今的分布格局。

Genetic variation and geographicial differentiation of Cytochrome b gene of Clawed jird ( Meriones unguiculatus )

In order to investigate genetic structure and population history of Meriones unguiculatus,a total of 1 140 base pairs(bp)of the mitochondrial Cyt b gene were sequenced from 52 individuals of six populations in the arid regions of China.Among the sequences of 1 140 bp,74 nucleotide sites were variable,including 65 transitions and 9 transversions.Significant genetic subdivision existed between Baotou population and the other populations,however not among other populations.A total of 37 haplotypes were detected and phylogenetic analyses recovered two distinct clades(Clade A and Clade B).Clade B consisted of tree haplotypes from the Eastern Helan Mountains population,the other haplotypes were in Clade A.A unimodal mismatch distribution of the Clade A was observed,and the Tajima's D test and Fu test were all significantly negative(D=-1.86,P<0.05 and Fs=-21.89,P<0.05),and suggests that a population colonization and expansion of M.unguiculatus occurred.The expansion times were estimated as 0.011 million years ago at the last interglaciation stage.The climatic oscillation during the Quaternary ice ages might resulted in the intra-specific divergences(Clades A and B)and the Eastern Helan Mountains might have served as a glacial refugium and harbored both distinct lineages.The present distribution of this species was probably shaped through the rapid range expansion from the refugium during the last interglaciation stage.