基于COⅠ基因片段的中国南部沿海近亲拟相手蟹的群体遗传多样性研究

为了研究我国南部沿海近亲拟相手蟹(Parasesarma affine)的群体遗传结构，本研究对12个地理群体共222个个体的线粒体DNA的细胞色素氧化酶亚基Ⅰ (COⅠ)基因片段进行了分析。结果表明，612 bp的COⅠ基因片段检测到34个变异位点，共定义了40个单倍型，其中Hap2为12个群体的共享单倍型，占个体总数的69.81%。总群体的单倍型多样性水平H_d为0.508 9，核苷酸多样性水平P_i为0.001 126，表现出中等水平的H_d和低水平的P_i。单倍型邻接发育树和单倍型中介网络图没有形成明显的地理系谱结构。近亲拟相手蟹群体内的遗传距离为0.000 36～0.001 73，群体间的遗传距离为0.000 48～0.001 72。群体间的遗传分化系数(F_st)和分子方差分析(AMOVA)结果表明，近亲拟相手蟹群体遗传分化水平低，其变异主要来自群体内。中性检验和核苷酸不配对分布结果提示，近亲拟相手蟹近期经历了群体扩张事件，扩张时间大约发生于5.1万年前的更新世晚期。研究表明，较长的幼虫浮游期以及海洋环境中缺少影响群体扩散的屏障可能是近亲拟相手蟹各地理群体间能进行广泛的基因交流，从而表现出较低的遗传分化水平的重要原因，更新世的剧烈气候变迁亦可能对其群体的遗传结构和分布格局产生影响。研究结果为近亲拟相手蟹自然资源的保护及合理开发利用提供了一定理论依据。

Genetic diversity of Parasesarma affine from the South China Sea based on mitochondrial DNA COⅠ gene

In this study,the population genetic diversity and structure of Parasesarma affine in the South China Sea were analyzed based on 222 individuals of twelve populations using Cytochrome OxidaseⅠ(COⅠ)sequence.A 612 bp fragment of COⅠgene were sequenced,from which 34 polymorphic sites were tested and 40 haplotypes were defined.The most frequent haplotype was Hap2 with the highest frequency of 69.81%,which was shared in all twelve populations.Total haplotype diversity(Hd)and nucleotide diversity(Pi)were 0.5089,0.001126,respectively,which represented a moderate level of haplotype diversity and a low level of nucleotide diversity.No clustering corresponding to sampling localities was found in neighbor-joining tree and haplotype network.The genetic distance ranged from 0.00036 to 0.00173 within populations and from 0.00048 to 0.00172 between populations.Genetic fixation index(Fst)and analysis of molecular variance(AMOVA)indicated that the genetic variance mainly came from individuals within populations,and a low level of genetic differentiation among twelve populations.Both neutral test and mismatch-distribution analysis implied that the populations of P.affine had a recent population expansion event that occurred in about 51000 years ago in the late Pleistocene epoch.In summary,the longer time of the planktonic larval phase and the lack of evident geographical barriers in the marine realm might be major reasons for that P.affine could carry out extensive gene flow and possessed a low level of genetic differentiation among all twelve populations.In addition,the severe climate change of pleistocene epoch might also have important effects on the genetic structure and patterns of distribution of P.affine populations.The research results could provide a theoretical basis for the conservation and utilization of P.affine.