The freshwater fish genus Thymallus (Thymallidae) in the upper OB-Irtysh River: its evolutionary history and implications for conservation

Quaternary geological and climatic events in central Asia have influenced the evolutionary history of populations of endemic species, and patterns in their distribution. We investigate species of grayling ( Thymallus ) from the upper OB-Irtysh River, Xinjiang, China, using mitochondrial DNA sequences and 10 microsatellite markers. Phylogenetic analyses attribute this species to Thymallus brevicephalus , and validate its divergence from a sister taxon, the Mongolian grayling ( Thymallus brevirostris ) through geomorphological changes caused by uplift of the Altai Mountains. Microsatellite analysis using STRUCTURE and pairwise FST analysis reveals significant genetic differentiation between eastern and western T. brevicephalus populations, which we estimate to have diverged approximately 0.81 million years ago (MY). High haplotype and low nucleotide diversities, and patterns of population history, indicate the western population of T. brevicephalus has slowly expanded following the Last Glacial Maximum approximately 0.4–0.1 MY. Hardy–Weinberg disequilibrium and within-population inbreeding coefficients identify a founder effect in this species. The origin of T. brevicephalus corresponds to the uplift of the Altai Mountains. Simultaneously, internal differentiation and population expansion occurred during repeated Quaternary climatic glacial–interglacial cycles. If management of T. brevicephalus , an endemic fish species in the upper Irtysh River in the Altai Mountains, was an option, we recommend establishing two management units separated by the Crane River. Release activities should be carried out independently for the eastern and western populations, and international cooperation in conservation efforts should be strengthened.