基于线粒体Cyt b基因的南海北部金钱鱼种群遗传结构分析

【目的】分析南海北部金钱鱼（Scatophagus argus）遗传多样性，明确其群体演化历史和分布动态，为金钱鱼养殖育种及其种质资源的合理开发利用提供科学依据。【方法】以采自福建东山（DS）、广东阳江（YJ）、海南海口（HK）、广西北海涠洲岛（BH）、广西钦州（QZ）、广西防城港（FC）及越南清化（TH）等南海北部的7个金钱鱼地理群体为研究对象，基于线粒体DNA细胞色素b基因（Cyt b）序列分析，利用DnaSP 5.10统计南海北部金钱鱼群体的单倍型、单倍型多样性指数（H_d）和遗传多样性指数（π），通过邻接法（NJ）构建单倍型的系统发育进化树，以Network 4.6中的中介连接网络法构建单倍型网络图，并综合Tajima’s D检验、Fu’s Fs检验及核苷酸错配分布等方法分析金钱鱼群体的历史动态。【结果】7个金钱鱼地理群体的291条Cyt b基因序列定义为33个单倍型（Hap1~Hap33），其中单倍型Hap1、Hap2和Hap7是南海北部金钱鱼在长期进化过程中形成的稳定优势基因型。7个金钱鱼地理群体的H_d为0.54103~0.77436，π为0.00112~0.00171，群体内遗传距离为0.00113~0.00171，遗传分化系数（F_st）为-0.01734~0.00364，基因流（Nm）为137.03888~inf。不同地理群体的单倍型均无规律地散布在单倍型系统发育进化树上，不存在与地理群体明显对应的系统分支，也未表现出明显的地理聚群分布特征。金钱鱼群体内个体间的遗传变异为100.74%，说明遗传变异全部来源于群体内个体间，即南海北部金钱鱼群体既无群体分化，也无以琼州海峡分隔的组群分化。Tajima’s D检验和Fu’s Fs检验结果均为显著负值，且核苷酸错配分布呈单峰分布，推测南海北部金钱鱼群体发生过群体扩张，且扩张事件约发生在3.4万年前，属于更新世晚期。【结论】南海北部7个金钱鱼地理群体的遗传多样性符合高单倍型多样性低核苷酸多样性类型，群体间遗传距离较小，亲缘关系较近，遗传分化不明显，且群体间存在频繁的基因交流，具有高度的遗传同质性，符合南海北部金钱鱼是一个随机交配种群的假设。

Genetic structure of the spotted scat(Scatophagus argus) populations in the northern South China Sea based on mitochondrial Cyt b gene

【Objective】In order to analyze the genetic diversity of the spotted scat(Scatophagus argus) in the northern South China Sea, clarify its population evolution history and distribution dynamics, and provide a scientific basis for the breeding, sustainable use of resources, and genetic diversity protection.【Method】The seven geographic S. argus populations collected in Dongshan, Fujian(DS), Yangjiang, Guangdong(YJ), Haikou, Hainan(HK), Weizhou Island, Beihai, Guangxi(BH), Qinzhou, Guangxi(QZ), Fangchenggang, Guangxi(FC), and Qinghua of Vietnam(TH) of the northern South China Sea were used as research objects. Based on the mitochondrial DNA cytochrome b gene(Cyt b) sequence analysis, DnaSP 5.10 was used to calculate the haplotype, haplotype diversity index(H_d), and genetic diversity index (π) of S. argus populations in the northern South China Sea. A phylogenetic tree of haplotypes was constructed by the neighbor joining method(NJ), a haplotype network diagram was constructed by the intermediary connection network method in Network 4.6, and the historical dynamics of S. argus populations was analyzed by the Tajima's D test, Fu's Fs test and nucleotide mismatch distribution methods.【Result】The 291 Cyt b gene sequences of the seven S. argus populations were defined as 33 haplotypes(Hap1-Hap33), among which haplotypes Hap1, Hap2 and Hap7 were stable dominant genotype formed during the long-term evolution of S. argus in the northern South China Sea.The H_d, π, genetic distance, genetic differentiation coefficient(F_st), and gene flow(Nm) of the seven geographic populations were 0.54103-0.77436, 0.00112-0.00171, 0.00113-0.00171,-0.01734-0.00364, 137.03888-inf, respectively. The haplotypes of different geographic populations were scattered irregularly on the haplotype phylogenetic tree, there was no systematic branch that clearly corresponded to a geographic population, and it did not show obvious geographic clustering distribution characteristics. The genetic variation among individuals within S. argus populations was 100.74%, indicating that all genetic variation came from individuals within populations, i.e., S. argus populations in the northern South China Sea had neither population differentiation nor group differentiation separated by Qiongzhou Strait. Both Tajima's D and Fu's Fs tests were significantly negative, and the nucleotide mismatch distribution was unimodal, indicating that S. argus populations in the northern South China Sea might have experienced an expansion event in history, which occurred about 34000 years ago, belonging to the late Pleistocene.【Conclusion】The genetic diversity of the seven geographic S. argus populations in the northern South China Sea belong to the diversity type of high haplotype diversity and low nucleotide diversity. The genetic distance between the populations is small, the genetic relationship is close, the genetic differentiation is not obvious, and there are frequent gene exchanges between populations and a high degree of genetic homogeneity, which is consistent with the hypothesis that S. argus in the northern South China Sea is a random mating population.