Conclusion
This study confirmed the existence of two genetically differentiated populations that showed strong parallel evolution. Such genetic parallelism was likely due to similar temperature environments. We identified population-specific genes that may be related to adaptations to high and low temperatures. These genes can be potential candidates for further exploration of the underlying mechanisms involved in confronting various challenges. In conclusion, by comparing the whole genomes of S. japonica populations from environments with different temperatures, we revealed various genes associated with local adaptations of this species to cold- and high-temperature environments. Specifically, the candidate genes were functionally related to membrane fluidity in cold environments and the cytoskeleton in high-temperature environments. These results advance our understanding of the underlying genetic mechanisms that allow rapid adaptations of fish species, particularly small ruminants, to survive in extreme environments.