Landscape determinants of genetic structure for Schizopygopsis younghusbandi in the Yarlung Tsangpo River drainage, Tibetan Plateau

Unraveling the drivers that shape landscape genetics could help better understand the relationship between genetic structure and environmental factors and provide a scientific basis for wildlife conservation and habitat management. In this study, a typical coldwater fish on the Tibetan Plateau, Schizopygopsis younghusbandi, was selected to explore its spatial genetic structure and the determinant factors using mitochondrial cytochrome b gene as the molecular marker. The results showed a total of 80 haplotypes and 90 variable sites among 663 individuals from 25 geographical populations, with haplotype diversities (Hd) ranging from 0.636 to 0.936 and nucleotide diversities (Pi) ranging from 0.00160 to 0.00450. Significant positive correlations were observed between Hd and spatial factors (longitude and elevation) as well as the majority of single or combined bioclimatic factors. The correlations between Pi and these factors were inconclusive, revealing that Hd was more sensitive than Pi to population dynamic fluctuations. The phenomenon of greater genetic diversity in higher, colder and drier areas was consistent with the central-marginal hypothesis for this highland-origin species. The majority of genetic differentiation indices Fst indicated moderate differentiation, showing genetic heterogeneity among geographical populations. Fst was positively correlated with variations of elevation and the first principal component of bioclimatic factors, showing a weakly positive relationship with river-network distance, which demonstrated that the Isolation-by-Environment model could explain this genetic structure. In conclusion, as a highly specialized coldwater fish, S. younghusbandi retained higher genetic diversity in higher, colder and drier areas, and population differentiation was mostly related to differences of local bioclimate. For future conservation, we advocate that different geographical populations be treated as separate conservation units, with close attention paid to marginal populations, which are more vulnerable to external disturbances and exhibited less genetic variation.