High intra-population genetic variability and inter-population differentiation in a plateau specialized fish, Triplophysa orientalis

Triplophysa orientalis (Herzenstein) is one of the Nemacheilinae (Cypriniformes: Balitoridae) fish species distributed in the Tibetan Plateau area. In order to understand the impact of plateau uplift on population history and the isolation effect of plateau lakes on T. orientalis, we examined its genetic structure and phylogenetic relationships. A total of 98 individuals from five wild populations, three from plateau lakes and two from branch rivers in upper reaches of the Yangtze River, in the eastern peripheral of the Tibetan Plateau were sampled. An 848 base pair fragment from the mitochondrial DNA (mtDNA) control region was sequenced for analyses. Overall, very high intra-population genetic variability was found in all populations except for one lake population (Rannicuo); nucleotide diversity ranged from 0.0025 to 0.0159 and haplotype diversity ranged from 0.641 to 0.879. Furthermore, the genetic distance between river populations (0.0326) was much higher than that among lake populations (Rannicuo and Barencuo 0.0035, Bannicuo and Yibicuo 0.0038, Rannicuo and Yibicuo 0.0049). Additionally, the analysis of molecular variance demonstrated that most of the observed genetic variability occurred among populations, accompanied with significant Fst values except for that between the Yibicuo and Barencuo populations. This evidence suggested a strong population structure of the species and a lack of inter-population connection. Lastly, the rate of migration indicated there were large historic gene flows among lake populations. Demographic analysis also indicated there were bottlenecks or expansions in three lake populations, suggesting a potential isolation effect of plateau lakes on population differentiation. Molecular dating of intra-specific divergence showed the plateau uplift has shaped the genetic structure of T. orientalis.