内蒙古地区布氏田鼠种群MHCⅡ类基因第二外显子的遗传分析

Genetic Analysis of Brandt′s Vole(Lasiopodomys Brandtii)Population Based on MHC Class Ⅱexon 2 in Inner Mongolia

以MHCⅡ类基因第二外显子(MHC classⅡexon 2)为分子标记,用限制性酶切多态性和直接测序的方法对分布于内蒙古地区的8个布氏田鼠种群共460个个体进行种群遗传结构的分析.结果显示,酶切共检测到6个等位基因,13个酶切多态性位点,卡方检验显示,各种群在6个酶切多态性位点上基因型频率不符合Hardy-Weinberg平衡.序列分析显示,在长度261 bp的核苷酸序列中,有57个变异位点,定义21种单倍型,其中有1个单倍型为不同区域种群所共享,其余20个单倍型均为各区域种群所特有.7个地理种群的单倍型多样性和核苷酸多样性较高,1个地理种群较低.谱系分析显示,8个布氏田鼠地理种群分为3个进化分支,分别与采集的地理种群相吻合:同一地理种群内单倍型之间遗传差异小,而不同地理来源的单倍型之间存在较大区别.Mentel检测表明,布氏田鼠的遗传分化与地理距离呈现正相关.AMOVA分析结果同样表明地理种群之间存在差异:各区域类群间变异组分占总变异比率的60.48%,区域内种群间变异组分占总变异比率的7.78%,种群内个体间变异组分占总变异比率的28.14%;遗传分化系数和基因流分析显示,布氏田鼠种群出现一定程度的分化,但正镶白旗种群与其他种群之间遗传分化显著.布氏田鼠的这种遗传结构特点可能是该物种稳定的地下生活环境和有限的迁移造成的,且浑善达克沙漠形成布氏田鼠分化最强烈的隔离因素.

The genetic diversity and genetic structure of 8 geo-populations of Lasiopodomys brandtii were ana-lyzed using PCR-RFLP and sequences analysis based on MHC class Ⅱexon 2. The Results showed that 6 al-leles and 13 polymorphic loci were detected. The Chi-square test results argued that genotype frequencies in6 polymorphic loci were not consistent with the Hardy-Weinberg equilibrium. 21 haplotypes were definedbased on 57 bases mutations,and one haplotype was shared by all populations. Haplotype diversity（H）andnucleotide diversity（πn）of 7 of L.brandtii populations were higher and another was relatively lower. The UP-GMA phylogenetic tree showed that the 8 geo-populations clustered into three groups,corresponding well totheir geographical distributions. Mantel test confirmed that genetic differentiation was positively correlatedwith the geographic distance. Analysis of molecularvariance（AMOVA）similarly recovered the distinct differ-entiation between geographical populations：regional genetic variation accounted for 60.48%,intraregionalpopulation variation accounted for 7.78%,and individual variation accounted for 28.14%. Analysis of geneflow and FSTsuggested that genetic differentiation already occurred among the 8 populations,but a high levelwas detected between the Zhengxiangbaiqi and other populations. The unique genetic structure of this spe-cies was probably the limited dispersal as well as the stable habitats of the subterranean living,and HunShan Da Ke Desert played the most important role in population differentiation of L.brandtii.