基于Cyt b基因序列的南海北部蓝圆鲹群体遗传多样性研究

Genetic diversity analysis of Decapterus maruadsi from northern South China Sea based on mitochondrial DNA Cyt b sequence

为了解南海北部蓝圆鲹(Decapterus maruadsi)的群体遗传变异特征,本研究利用线粒体DNA Cyt b基因部分序列对9个群体共203个个体进行群体遗传多样性和遗传结构分析.结果显示:在722 bp长的Cyt b部分序列中,共检测出52个多态位点,定义25个单倍型;群体的单倍型多样性(h)为0.577±0.036,核苷酸多样性(π)为0.001 55±0.001 12,整体遗传多样性呈中等偏低水平,其中雷州半岛和海南岛以东5个群体的遗传多样性水平明显高于以西的4个北部湾群体.单倍型系统发育树和网络图均未表现出与地理位置相对应的谱系结构,单倍型网络图呈以主体单倍型为中心的星状结构.群体间的Fst值为-0.077~0.018,且统计检验均不显著(p>0.05).分子方差分析(AMOVA)表明,遗传变异全部来源于群体内个体间.Tajima's D值和Fu's Fs值均为显著负值,核苷酸不配对分布呈明显的单峰分布.南海北部蓝圆鲹群体约在29 000a前可能发生过扩张事件,导致遗传多样性呈现高h、低π模式;9个群体间的遗传分化并不显著,符合是一个随机交配种群的假设,但9个群体的遗传多样性水平却表现出明显的地理趋势,提示将南海北部蓝圆鲹作为单一种群进行渔业管理需持谨慎态度.

The round scad,Decapterus maruadsi,is a commercially important species in northern South China Sea.However,the catches of the species has declined severely. Thus,there is a strong need to study the population genetic of D. maruadsi in northern South China Sea for the effective conservation and sustainable fishery management. In this study,genetic diversity and genetic structure of D. maruadsi in northern South China Sea were analyzed based on 203 individuals of 9 populations using mitochondrial DNA cytochrome b（Cyt b） sequence. A 722 bpsegment of mt DNA Cyt b gene was sequenced,which revealed 52 polymorphic sites and defined 25 haplotypes. The haplotype diversity and nucleotide diversity were 0. 577 ± 0. 036 and 0. 001 55 ± 0. 001 12,respectively,which indicated that genetic diversity of D. maruadsi in northern South China Sea was low to moderate. Five populations in the east of Leizhou Peninsula and Hainan Island showed higher level genetic diversity than 4 populations in the west. No clustering corresponding to sampling localities was found in Bayesian inference tree,neighbor-joining tree,and haplotype network. The haplotype network was star-like with two dominant haplotypes surrounded by other low-frequency haplotypes. The pairwise Fst values between nine populations ranged from-0. 077 to 0. 018 and showed no significant genetic difference. Analyses of molecular variance（AMOVA） revealed that all genetic variations were attributable to the variations among individuals within populations. Both Tajima＇s D（D =-2. 602,p =0） and Fu＇s Fs（Fs =-23. 376,p = 0） yielded significant negative values. Unimodal distributions were observed for the total population. The results suggested D. maruadsi from northern South China Sea had experienced a population expansion at about 29 000 years ago,which was responsible for the genetic diversity model with high h value and low π value. Genetic structure analysis revealed that there was no significant genetic differentiation among nine populations,which indicated that D. maruadsi from northern South China Sea was consistent with the hypothesis of a panmictic population. However,the obvious geographic tendency of genetic diversity was detected among nine populations. The inconsistent reminded us to cautiously manage the populations of D. maruadsi in northern South China Sea as a ‘one stock＇.