Chromosome-level genome assembly and population genomic analysis provide insights into the genetic diversity and adaption of Schizopygopsis younghusbandi on the Tibetan Plateau

The Yarlung Tsangpo River on the Tibetan Plateau provides a unique natural environment for studying fish evolution and ecology. However, the genomes and genetic diversity of plateau fish species have been rarely reported. Schizopygopsis younghusbandi, a highly specialized Schizothoracine species and economically important fish inhabiting the Yarlung Tsangpo River, is threatened by overfishing and biological invasion. Herein, we generated a chromosome-level genome of S. younghusbandi and whole-genome resequencing data for 59 individuals from six locations of the river. The results showed that the divergence time between S. younghusbandi and other primitive Schizothoracine species was similar to 4.2 Mya, coinciding with the major phase of the Neogene Tibetan uplift. The expanded gene families enriched in DNA integration and replication, ion binding and transport, energy storage, and metabolism likely contribute to the adaption of this species. The S. younghusbandi may have diverged from other highly specialized Schizothoracine species in the Zanda basin during the Pliocene epoch, which underwent major population reduction possibly due to the drastic climate change during the last glacial period. Population analysis indicated that the ancient population might have originated upstream before gradually adapting to evolve into the populations inhabiting the mid-stream and downstream regions of the Yarlung Tsangpo River. In conclusion, the chromosome-level genome and population diversity of S. younghusbandi provide valuable genetic resources for the evolution, ecology, and conservation studies of endemic fishes on the Tibetan Plateau.