凤鲚两群体线粒体细胞色素b基因片断多态性及进化特征

为研究凤鲚（Coilia mystus）的长江群体和珠江群体的遗传多态性、遗传关系及进化特征,使用线粒体DNA（mitochondrial DNA,mtDNA）的细胞色素b（cytochrome b,cytb）基因片断序列进行分析.在该基因片断上共检测到44个变异位点,总变异率为11.5%.凤鲚长江群体内部的遗传距离为0.3%～1.0%,珠江群体内部的遗传距离为0.5%～0.8%,长江群体与珠江群体之间的遗传距离为9.4%～10.9%.这2个群体具有完全不相同的单倍型,其中长江群体5个个体中共检测到5种不同的单倍型,单倍型多样性指数为1.000,核苷酸多样性指数为0.677%;珠江群体5个个体中共检测到4种单倍型,单倍型多样性指数和核苷酸多样性指数分别为0.900和0.573%.对两者序列的自然选择检验分析表明,自然选择在两者差异形成过程中起重要的作用.中国水产科学,2006,13（3）：337-343]

Genetic diversity and evolutionary characters in two populations of Coilia mystus inferred from cytochrome b gene segment sequence of mitochondrial DNA

Coilia mystus is distributed mainly in the northern Indian Ocean and the western Pacific Ocean,extending eastward to China,Korea and Japan,and Southward to Indonesia.It is classified into genus Coilia(Gray,1831),Engraulidae,Clupeiformes.Some differences maybe exist between different populations of C.mystus due to isolation and adaption.The great morphological differences between two geographical populations of C.mystus,Yangtze River population and Pearl River population,were revealed by multivariate analysis.In general,fishes demonstrate greater variance in morphometric traits both within and between populations than other vertebrate,and are more susceptible to environmentally-induced morphological variation.Thus,it is necessary to reveal the differences between different geographical populations by using stable molecular markers.Genetic diversity and evolutionary characters in two populations of Coilia mystus,Yangtze River population and Pearl River population,were investigated at the mtDNA level in this study.A total of ten fish,i.e.,five fish at each site,were collected.Sequences of cytochrome b (cytb) gene segments amplified by PCR was used.Fourty-four variable sites were detected,accounting for 11.5% of total sequence.Genetic distances within the Yangtze River population were between 0.3% and 1.0%,within the Pearl River population were between 0.5% and 0.8%,and genetic distances between Yangtze River population and Pearl River population were from 9.4% to 10.9%.The large genetic distances between these two populations suggest their divergence maybe arrived at subspecies level.Five different haplotypes were detected within Yangtze River C.mystus and four within Pearl River C.mystus.The haplotype diversity index of Yangtze River C.mystus and Pearl River C.mystus were 1.000 and 0.900,respectively.The nucleotide diversity of Yangtze River population and Pearl River population were 0.677% and 0.573%,respectively.These indexes suggest that these two populations of C.mystus are abundant in genetic diversity.Two methods,K_a/K_s test and McDonald-Kreitman test,were used to detect if natural selection operated at DNA level during the formation of divergence between these two populations.Significant results were revealed by the two methods(the ratios of K_(a)/K_(s)are all less than 1 and the G value and P value of MK test is equal to 6.715 and 0.009?56,respectively),and it suggests that natural selection operates on this gene during its evolution.The cytb gene is an important gene in mitochondrial DNA,and severe diseases can be caused once the nonsynonymous substitution happens in this gene.Due to natural selection,the individual which has this damaged gene can not be fixed in the population and was removed from this population.Thus,it is reasonable to observe the action of natural selection.