基于线粒体基因标记的中西太平洋鲣群体遗传学分析

Population genentic structures of Katsuwonus pelamis in the Western-Central Pacific Ocean based on mitochondrial genes

为了解中西太平洋鲣(Katsuwonus pelamis)群体间的遗传结构和不同群体间的遗传分化,采用线粒体细胞色素b基因(Cytb)和细胞色素氧化酶Ⅰ(COⅠ)基因序列对中西太平洋3个区域共112尾鲣样本进行群体遗传学研究。由Cytb和COⅠ基因序列测得的单倍型多样性指数(Hd)分别为0.997和0.943,而核苷酸多样性指数(Pi)分别为0.0100和0.00268,来源于种群内的变异分别达到了99.50%和100.64%,两两群体间的遗传分化系数Fst值均小于0.05,P值均大于0.05,且基因流Nm远大于1。结果表明,3个鲣群体间不存在显著的遗传分化,且具有频繁的基因交流。中性检验和核苷酸错配分布曲线结果显示,鲣可能在末次冰期经历快速的群体扩张事件。由于推算的鲣群体扩张时间与历史海平面变动存在相关性,推测中西太平洋鲣种群的扩张极有可能与海平面的快速上升(海侵)有关。综上所述,中西太平洋鲣未出现显著分化的地理群体,建议在渔业管理上将3个地理群体视为一个统一的管理单元。

Skipjack tuna Katsuwonus pelamis,one of the most important tuna species,is widely distributed in the tropical and temperate oceans.In order to understand and manage this fishery resource more scientifically and reasonably,it is required to obtain its population genetic structure and genetic differentiation.To our knowledge,there are limited studies on genetic diversity of K.pelamis in the Western-Central Pacific Ocean.And a single genetic marker has been unable to meet the research demands of genetic diversity.In our study,the genetic relationships of K.pelamis individuals collected from three zones in the Western-Central Pacific Ocean were measured by sequence analysis of cytochrome b(Cytb)and mitochondrial cytochrome c oxidase subunit I(COⅠ)genes.The genetic relationship among 112 K.pelamis sampled from three zones in the Western-Central Pacific Ocean were studied.A fresh piece of back muscle tissue of approximate 2 cm in length was extracted from each individual and placed in ethanol for DNA-based analyses.For each sample,the PCR reaction was carried out in a total volume of 25μL containing 1μL DNA template,5 XPS 5μL,PrimerSTAR MAX 0.5μL,dNTPs 2μL,forward and reverse primers 0.5μL each,and double distilled water 16 L.PCR was performed with initial denaturation at 95℃for 2 min,followed by 30 cycles of 95℃for 60 s,50℃for 30 s and 72℃for 90 s,and a final extension at 72℃for 5 min.Sequences were aligned in MEGA 7.0 with ClustalW and collapsed into haplotypes.Genetic diversity indices were estimated for each lineage in DnaSP6.12,including the number of haplotypes(H),haplotype diversities(Hd),nucleotide diversities(Pi)and gene flow(Nm).Analysis of genetic population differentiation was performed using a pairwise comparison Fst in Arlequin3.5.2.For each lineage,neutrality tests and population demographic changes also were calculated,including Tajima’s D,Fu’s Fs.The time of expansion(T)in years(with the broad assumption of 1-year-generation time)was calculated from T=t×Tau/4kμ.Results suggested that there were 112 Cytb sequences with a 1059 bp alignment matrix yield 98 different haplotypes,and 106 COⅠsequences with a 1205 bp alignment matrix yield 52 different haplotypes.The haplotype diversity and nucleotide diversity of three populations of K.pelamis were 0.997 and 0.0100 by Cytb sequences,0.943 and 0.00268 by COⅠsequences,respectively.The genetic variation observed within populations was 99.50%and 100.64%,respectively.Fst was less than 0.05,P values were higher than 0.05,and Nm was far more than 1.The expansion time of K.pelamis was estimated using Cytb sequences(78800 years ago)and using COⅠsequences(67,400 years ago to 22,500 years ago).Median-joining network showed that haplotypes were correlated with each other,and there was no independent haplotype corresponding to these three regions.The frequent gene exchange among three populaitons were revealed without obvious genetic differentiation.The neutrality test and nucleotide mismatch distribution curve indicated that the K.pelamis had experienced rapid population expansion during the last Ice Age.The estimated time of population expansion of K.pelamis was correlated with the historical changes of sea level.Therefore,it was speculated that the population expansion was probably related to the rapid rise of sea level(transgression).In summary,there is no distinct geographic population of K.pelamis in the Western-Central Pacific Ocean,suggesting that these three geographic populations could be assessed and managed as an integration unit during the conservation and management for this important fishery.