基于线粒体Cyt b序列的雅砻江长丝裂腹鱼群体遗传结构分析

该研究测定了2018年间采集于雅砻江干流甘孜、雅江、锦屏和金河江段的4个长丝裂腹鱼野生群体共118尾个体的线粒体细胞色素Cyt b基因全序列，以评估其遗传多样性和遗传结构。结果显示：118条长丝裂腹鱼序列共定义了19个单倍型，29个多态位点，总群体单倍型多样性指数（Hd）为0.850 ± 0.017，核苷酸多样性指数（π）为0.003 35 ± 0.001 89，各群体Hd范围0.697 ± 0.069 ~ 0.831 ± 0.022，π范围0.000 92 ± 0.000 79 ~ 0.006 22 ± 0.003 36。中性检验结果表明，Tajima′s D 和Fu′s Fs均为显著性负值，单倍型核苷酸不配对分布呈典型单峰，表明雅砻江长丝裂腹鱼经历过种群扩张事件。分子方差分析（AMOVA）表明，84.84%的分子差异来源于群体内部，15.16%的分子差异来源于群体之间。FST值统计检验表明，除甘孜群体和雅江群体之间差异不显著外，其余两两群体之间FST值统计检验均显著。根据研究所揭示的雅砻江长丝裂腹鱼种群遗传结构特征，尽管群体之间存在显著的遗传分化，但分化水平仍属于种群内分化，建议将分布在雅砻江干流的长丝裂腹鱼作为一个整体进行保护。

Genetic structure of Schizothorax dolichonema (Herzenstein, 1889) in Yalong River revealed by mtDNA Cyt b sequences

Schizothorax dolichonem is an endemic fish species that mainly distributes in main streams and tributaries of the upper reaches of the Yangtze River in China. In the Yanglong River basin, S. dolichonem is one of the main catch objects, playing an important role in fishery production of Yanglong River. In recent years, many factors such as pollution, overfishing, damming, habitat degradation and environmental change, have seriously affect its natural resources, especially the cascade hydropower development in the middle and lower reaches of Yalong River. Fragmentation caused by hydropower stations may disrupt communication of fish populations and influence population genetic structure and diversity. A good understanding of population genetic structure would be useful for better conserving and restoring the natural resources of this schizothoracin. In present study, 118 individuals of S. dolichonem sampled from Ganzi, Yangjiang, Jinping and Jinhe sections of Yanglong River in the year 2018 were analyzed, using the complete mitochondrial cytochrome b gene sequences. The result showed that the length of Cyt b gene of was approximate 1085 bp. 19 haplotypes and 29 polymorphic sites were found among 118 S. dolichonem individuals. The total haplotype diversities (Hd) and nucleotide diversities (π) were 0.850 ± 0.017 and 0.003 35 ± 0.001 89, respectively. The Hd ranged from 0.697 ± 0.069 to 0.831 ± 0.022, and π from 0.000 92 ± 0.000 79 to 0.006 22 ± 0.003 36 among the four groups, respectively. Analysis of molecular variance (AMOVA) showed that most of the genetic variation occurred within groups (84.84%). The neutrality test and mismatch distribution indicated that the population of S. dolichonem in the Yanglong River had experienced an expansion. Pairwise fixation index (FST) values indicated significant differentiation between any two groups (FST ranged between 0.090 48 - 0.199 17, P < 0.05), except between Ganzi and Yangjiang groups (FST = 0.043 47, P > 0.05). Although significant FST values were found among geographical groups, the differentiation level still belonged to intra-population differentiation, suggested that these groups of S. dolichonem in Yanglong River should be considered as a single management unit. In conclusion, this study provided valuable information for restoration of S. dolichonem natural resources in Yanglong River and theoretic knowledge for a rational utilization of the germplasm resources.