中国近海路氏双髻鲨群体线粒体DNA控制区序列比较分析

Comparative analysis based on the mitochondrial DNA control region of Sphyrna lewini

采用线粒体DNA控制区序列比较分析了路氏双髻鲨日照和霞浦群体的遗传结构及遗传多样性现状。研究结果显示:在长度为548 bp的mtDNA控制区序列上,34尾路氏双髻鲨个体仅检测到5个单倍型,两群体均呈现出较低的遗传多样性水平,日照群体的单倍型多样度(h)、核苷酸多样度(π)以及两两序列比较的平均碱基差异数(p)(h=0.6000±0.1305;π=0.0046±0.0031;p=2.5333±1.4856)略高于霞浦群体(h=0.5109±0.0955;π=0.0024±0.0017;p=1.2899±0.8373);邻接关系树显示,5个单倍型明显分为两支,净遗传距离为0.016;群体遗传分化指数为Fst=-0.047(P=0.914),表明两群体之间不存在显著差异,确切P检验结果也表明两群体存在随机交配现象(P=0.731);核苷酸不配对分布呈双峰类型,其中一个峰对应类群内序列差异,另外一个峰对应两个类群序列间差异。研究表明,路氏双髻鲨较小的有效群体导致了较低的遗传多样性,其资源状况已不容乐观。

The scalloped hammerhead shark（Sphyrna lewini） is circumglobally distributed along continental margins and oceanic islands in tropical waters.With the development of fishery resource,S.lewini is one of the most affected and ecologically important species.It is very important to investigate the genetic variance and population structure of this species.However,there are no genetic investigations for this fish in China.In the present study,thirty-four individuals were collected to analyze the genetic diversity and genetic structure for this species.A 548 bp fragment of the hypervariable portion of the mtDNA control region was sequenced and sequences were edited and aligned.The fragments revealed 11 polymorphic sites,which defined 5 haplotypes.The results of present study showed that haplotype diversity,nucleotide diversity and mean number of pairwise differences of Rizhao population（h=0.6000±0.1305;π=0.0046±0.0031;p=2.5333±1.4856） were a little higher than those of Xiapu population（h=0.5109± 0.0955;π=0.0024±0.0017;p=1.2899±0.8373）.A Neighbour-Joining（NJ） tree of the control region haplotypes was constructed based on the outgroup S.zygaena and two haplotypes from East Pacific which were downloaded from NCBI.Two haplotypes from East Pacific were clustered with three haplotypes from the present study and two lineages were distinguished by 1.6% sequence divergence.The pairwise fixation index Fst=-0.047（P=0.914） revealed no significant genetic differentiation between two populations.The exact test of population differentiation（non-differentiation exact P values） following sequential Boferroni correction showed that no significant differences（P〈0.01） existed between two populations,which supported null hypothesis.The mismatch distribution analysis of all the S.lewini sequences was bimodal,and one small mode corresponded to internal clade comparisons and the other to differences between individuals among clades.Low levels of genetic diversity in Chinese Coast Sea for S.lewini may be a consequence of small effective population size which restricted gene flow.The results of present study provided a deeper understanding of the processes that led to existing levels and patterns of genetic diversity.