秦岭细鳞鲑群体遗传结构

秦岭细鳞鲑(Brachymystax lenok tsinlingensis)是秦岭地区特有鱼类,近年来由于环境恶化及人类活动的加剧,已对其造成严重影响,种群处于濒危状态,因此研究秦岭细鳞鲑的群体遗传结构、演化历史、分布动态等对其进行有效保护具有重要意义。本研究用线粒体D-loop区序列对秦岭地区6个群体(n=112)进行了遗传结构和群体演化分析。D-loop区扩增出的891bp序列在112个个体中,检测到42个变异位点,共26个单倍型;碱基序列总的单倍型多样度较高为0.883,核苷酸多样度为0.00799。AMOVA分析显示,60.05%的分子差异位于群体内,39.95%的分子差异位于群体间,Fst值统计检验表明,除那布大河群体与漳河群体和千河群体之间差异不显著之外,其余两两群体之间Fst值统计检验均为显著。系统树和单倍型网络图分析表明,6个地理群体的单倍型按照渭河上游和渭河中游两个河段形成两个大的类群,且5个群体共享一个单倍型H2,表明这些群体具有相同的演化历史,为同一个祖先群体演化而来。中性检验和歧点分布显示,秦岭细鳞鲑种群大小保持相对稳定,未经历明显的种群扩张。同时建议将渭河上游秦岭细鳞鲑群体作为一个整体进行重点保护。

Population genetic structure of Brachymystax lenok tsinlingensis as inferred from mtDNA D-loop sequence

Brachymystax lenok tsinlingensis is one of an endemic fishes distributing in Qinling mountains scatteredly. Due to environmental depravation and overfishing, its population size was sharply decreased. To establish a scientific basis to conserve this species, studies on the population genetic structure and phylogeography are necessary. In this study, the population genetic variations and phylogeographical patterns of 112 Brachymystax lenok tsinlingensis collected from six sites of the Wei River basin were investigated. An 891bp control region partial sequence of mtDNA was amplified in each sample, and 42 variable sites were detected, including 39 parsim-info sites and 3 singleton sites, with 26 haplotypes. The contents of cytosine, thymine, adenine and guanine were 23.1%, 30.8%, 31.7%, and 14.5%, respectively. Total haplotype diversity and nucleotide diversity were 0.883 and 0.00799, respectively. The genetic diversity of the Malu River population was the highest among these six populations, while the population of Zhang River was the lowest with only one haplotype H2. Of the 26 haplotypes, H2 was detected in 35 samples (31%) from 5 populations except the Malu River population. The result of AMOVA showed that 39.95% molecular variation was among populations and 60.05% within populations. The pairwise fixation index (F_st) revealed significant differences except between the Zhang River population and the Nabuda River population. Phylogenetic tree with Hucho taimen as outgroup showed that three geographic populations from the middle reach of Wei River including 16 haplotypes formed a big branch, and the rest haplotypes formed several small branches. The minimum spanning network for Brachymystax lenok tsinlingensis showed that the haplotypes of six geographical populations formed two big groups: the upper reach group and the middle reach group of the Wei River. The haplotype H2 was inner branch haplotype, it tend to be more widely as the ancestors haplotype, thus Brachymystax lenok tsinlingensis may have originated in the haplotype H2. Mismatch distribution analysis map showed a peak type, and Tajima's D value (-0.18715) of neutrality test is negative, but no significant difference, which indicates that Brachymystax lenok tsinlingensis in this research hadn't experience population expansion. Maybe due to climate change, the remaining individuals do not adapt to the living environment, the population don't carry out expansion. The haplotype H2 derives to the other haplotype in the different environmental, Wei River was cut off by a large number of water-shore projects, the migratory route is blocked, it was distributed with dots along the Wei River basin, lacked gene exchange between among populations. Due to the low level of genetic variation of three populations in the Wei River upper reach, more attentions should be paid to protect Brachymystax lenok tsinlingensis as a whole population.