基于线粒体细胞色素b基因序列探讨长江流域斑点蛇种群遗传结构和地理分化

Population Genetic Structure and Geographic Differentiation of Saurogobio punctatus(Teleostei,Cypriniformes,Cyprinidae) in the Yangtze River Basin Based on Cytochrome b Gene Sequences

通过分析303尾来自长江上游赤水河、长江上游干流和长江中游的斑点蛇Saurogobio punctatus线粒体细胞色素b(Cyt b)基因序列,探讨这3个种群的遗传结构及地理分化过程。用于分析的Cyt b基因序列长1 097 bp,含变异位点80个,其中简约信息位点34个。303尾个体共检测到49个单倍型,整体呈现较高的单倍型多样性(H_d=0.803)和较低的核苷酸多样性(P_i=0.003 71)。由单倍型构建的系统发育树显示:所有来自长江中游种群的单倍型聚在一起,形成一个单系群,处于系统发育树最进化的位置;来自长江上游干流和赤水河种群的单倍型处于更基部的位置,不能构成单系群。长江上游干流种群与赤水河种群间具有较多的共享单倍型,二者间的遗传分化指数较低(F_(ST)=0.029 4),存在广泛的基因交流。而长江中游与长江上游干流及赤水河种群间的FST值分别为0.614 0和0.706 0,暗示长江上游与长江中游的斑点蛇间已发生高度分化。中性检验及错配分析显示,长江上游干流种群及赤水河种群经历过种群扩张,而长江中游种群未检测到扩张。Bayesian skyline plot(BSP)分析显示,斑点蛇种群从距今20万年前开始发生扩张,一直持续到末次间冰期(MIS5)晚期,而后迅速扩张。根据BSP分析及单倍型网络图,推测斑点蛇的起源中心可能在长江上游,然后通过种群扩张逐渐扩散到长江中游,进化成遗传分化较大的种群。

The population genetic structure and geographic differentiation process of 3 Saurogobio punctatus populations from the Chishui River（ one branch of the upper Yangtze River）,the upper Yangtze River main stream,and the middle Yangtze River were studied based on mt DNA cytochrome b gene sequences of 303 individuals. The analyzed cytochrome b gene sequences were 1 097 bp in length,with 80 variable sites including 34 parsimony informative sites. A total of 49 haplotypes were identified from 303 individuals,which showed high haplotype diversity（ Hd= 0. 803） and low nucleotide diversity（ Pi= 0. 003 71）,respectively. Based on haplotype dataset,phylogenetic trees which were constructed using neighborjoining,maximum likelihood and Bayesian inference methods showed that all haplotypes from the middle Yangtze River clustered together and formed a monophyletic group. This group locates in the derived position of the phylogenetic trees,whereas haplotypes from the upper Yangtze River main stream and the Chishui River failed to form a monophyletic group with relative basal positions in the phylogenetic tree. Extensive gene flow might exist between populations of the upper Yangtze River main stream and Chishui River since many haplotypes were shared by them with a low genetic differentiation index（ FST=0. 029 4）,indicating a close relationship. The FSTvalues between the middle Yangtze River and Chishui River populations,and between the middle Yangtze River and the upper Yangtze River main stream populations were 0. 614 0 and 0. 706 0,respectively,indicating a high level differentiation. Neutral test and mismatch analysis showed that both the populations of upper Yangtze River main stream and Chishui River had experienced population expansion,but not in the middle Yangtze River population. Bayesian skyline plot（ BSP） analysis showed that S. punctatus populations started the expansion from0. 20 Ma BP,and lasted until the end of the last interglacial period,the Marine Isotope Stage 5,then experienced a rapid expansion. According to BSP analysis and haplotype network,we inferred that the origination center of S. punctatus population may be the upper Yangtze River,and then gradually spread to the middle Yangtze River via population expansion,and eventually evolved into a distinct genetic population.