Phylogenetic relationships of graylings (Thymallus, Linck, 1790) in Mongolia based on mitochondrial DNA

Local to large-scale phylogenetic studies of freshwater fishes, especially groups with controversial within-genus diversity (e.g., Thymallus Linck, 1790), are crucial to understanding their phylogenetic statuses. We examined the phylogenetic relationships and evolutionary divergence of species in the genus Thymallus (grayling) in Mongolia using mitochondrial DNA. In this study, we used 124 samples from 15 sites in rivers and lakes in the western, northern, and eastern parts of Mongolia to clarify their phylogenetic relationships. Our Bayesian inference and maximum likelihood trees support the existence of seven species of graylings in Mongolia, including Thymallus brevirostris, Thymallus nigrescens, Thymallus svetovidovi, Thymallus grubii, Thymallus arcticus, and new for the country Thymallus brevicephalus and Thymallus baicalensis. We observed relatively close sister species relationships of T. brevirostris and T. brevicephalus (p distance: 0.4%), as well as T. nigrescens and T. baicalensis (p distance: 0.5%). We also ran a time-calibrated phylogenetic tree to trace evolutionary divergence between species and found a divergence time ranging from 0.87 to 7.24 million years ago. Better knowledge of within-genus diversity of fish in the rivers of Mongolia (including the upstream portions of larger river drainages and lakes that graylings populate) is key to further conservation of these species.