基于线粒体DNA序列的秦岭地区淡足青步甲种群遗传结构分析

淡足青步甲Chlaenius pallipes是一类重要的天敌昆虫。为了揭示秦岭地区淡足青步甲的种群遗传分化和种群历史动态,对13个地理种群151个个体的线粒体Cox1-tRNALeu-Cox2片段DNA序列进行了分析。序列比对后的全长为1 602 bp,共检测到57个多态性位点,定义65个单倍型,其中48个为居群内特有单倍型,17个为居群间共享单倍型。单倍型多样性指数H_d 为0.972,核苷酸多样性指数P_i为 0.0025。该种群遗传分化明显,但AMOVA分析结果表明变异主要来源于种群内,占变异总量的92.10%。SAMOVA和PERMUT分析结果均表明秦岭地区的淡足青步甲种群不存在明显的谱系地理结构。结合中性检验、错配分布和BSP分析结果表明该物种发生过种群扩张,且扩张时间大致在0.100-0.025 Ma之间。

Population genetic structure of the ground beetle Chlaenius pallipes from the Tsinling Mountains based on mitochondrial DNA analysis

The ground beetle, Chlaenius pallipes, belonging to the genus Chlaeniu (Coleoptera: Carabidae), is widely distributed in East Asia and overwinters as adults. It is highly abundant in northern China and plays an important role in agriculture and forest pest control. To understand the population genetic differentiation and demographic history of C. pallipes from the Tsinling Mountains, a 1,602 bp fragment of mitochondrial DNA (Cox1-tRNALeu-Cox2) was sequenced for 151 individuals from 13 geographical populations from Gansu, Shaanxi, and Henan provinces. Fifty-seven polymorphic sites were identified, of which 45 are parsimony informative, 11 singleton variable sites, and a 1 bp insertion. These polymorphic sites defined 65 haplotypes, among which 17 were common and 48 were private with relatively lower frequencies. The haplotype diversity (H_d= 0.972) was hight but the nucleotide diversity was low (P_i= 0.0025). The topologies of the phylogenetic trees obtained based on maximum likelihood (ML) and Bayesian inference were similar. Both ML tree and Bayesian inference tree revealed two clades (a and b) from node d on the trees. In the haplotype network, a five median vector was employed and several loops were constructed and"star phylogeny"patterns were present. Analysis of molecular variance (AMOVA) suggested that most of the variation was due to within-population differences (92.10%), while differences among populations only contributed 7.90% of the total. The among-population F_ST value was 0.07897 (P < 0.01). Consequently, we conclude that there is obvious genetic differentiation in the C. pallipes populations we investigated. For the spatial analysis of molecular variance (SAMOVA), increasing K values from 2 to 12 were selected; the F_CT values were fairly low and fluctuated. Thus, the SAMOVA tests failed to reveal any meaningful phylogeographic structure. Furthermore, the results of the PERMUT analysis did not suggest any phylogeographic structure of the populations sampled based on the mtDNA haplotype data, as total N_ST(0.114) was not significantly higher than G_ST(0.101; P > 0.05). The results of the neutrality tests on the total indicated that both the Tajima''s D and Fu''s F_S were negative values, and the tests for the values are highly significant (P < 0.01), suggesting demographic expansion. Mismatch distribution analysis revealed a unimodal frequency distribution of pairwise difference in the total population and in each haplogroup. Both the neutrality tests and mismatch distribution analysis suggested that this species has undergone a demographic expansion. Furthermore,we used the Bayesian Skyline Plot (BSP) approach to estimated the demographic history of C. pallipes under BEAST 1.4.7. The demographic expansion time was identified as being between 0.100 Ma to 0.025 Ma. We found evidence of constant population size before the end of the Last Glacial Maximum (LGM, between 0.020 and 0.018 Ma) developed in the Tsinling Mountains. Consequently, we suggest that LGM had little effect on the demographic dynamics of C. pallipes.