Genetic structure of Gymnodiptychus pachycheilus from the upper reaches of the Yellow River as inferred from mtDNA control region

Gymnodiptychus pachycheilus,one of the endemic Schizothoracin fishes,is peculiar to China and mainly distributed in plateau lakes and rivers of the Yellow River on the Northeast Qinghai-Tibetan Plateau.During the long evolutionary history,G.pachycheilus is characterized by slow growth rate,low fecundity,and late sexual maturation as adaptations to their rigorous environment.However,these life-history characteristics make it particularly sensitive to factors such as habitat destruction/alteration,climate change,biological invasions,pollution.Overexploitation is also likely to be having considerable effects on the species survival.To access the genetic diversity,genetic structure and population dynamics of G.pachycheilus,the control region DNA sequences of G.pachycheilus were checked and compared with the homologous sequences of 81 individuals,including 71 individuals from Maqu county,and 10 individuals retrieved from GenBank sampled from Guide county and Maduo county.And 729 bp length sequences were defined for 81 individuals.Sequence analysis results showed that there were only 26 variable sites,including 3 single variable sites and 23 parsimony informative sites.No site was found that had alignment gaps or missing data.The samples fall into 34 haplotypes,with only 0.844 haplotype diversity and 0.0054 nucleotide diversity.There was no geographic clustering observed in the haplotype network,haplotype H2 distributed most widely and on 32 samples(38.27%) from the Maqu county population.H2,H14,H23 were shared by all the three population.The median-joining network produced a complex pattern with no obvious phylogeographic structure.Although H2 was in the center,the network showed little evidence for overt phylogeographic structure and showed star-like radiation.The Fu′s Fs test,the distribution of pairwise differences and the network analysis indicate that G..pachycheilus in the research had experienced certain population expansion events,which is consistent with the hypothesis that the headwater area of the Yellow River was dramatically affected by the geological and climatic upheaval during the Pleistocene.Analysis of molecular variance(AMOVA) showed that 93.53% of the total genetic variance was contributed by the within groups variation and only 6.47% contributed by the among-groups variation(Fst= 0.0647,P0.05).Fst analyses produced similar results that significant Fst values were detected between Mq vs.Gd population.No significant(P0.05) genetic differences were found either within or between the different populations,indicating weak genetic structure among the three populations.Mismatch distribution and neutrality tests indicated that G.pachycheilus in this research had experienced population expansion.Our analysis indicated by mtDNA control region as the first approach to understand the genetic diversity of G.pachycheilus.We suggest that all the three populations should be managed and conserved as a whole.In situ conservation is first recommended to protect its original habitat from further destruction.The conservation of the unique habitat of G.pachycheilus is essential for the survival of the species.