Convergent Evolution Of Yak And Tibetan Antelope In Response To High-Altitude Stress

The Qinghai-Tibet Plateau(QTP), the world’s highest plateau, has an extremely harsh environment: it is cold, hypoxic, and exposed to high levels of ultraviolet radiation, factors which limit the ability of animals to thrive there. Native animals living on the QTP all display numerous similar traits that are adaptive to this highaltitude environment. Convergence often occurs when organisms with different ancestors adopt similar adaptations to environmental stresses. Yak(Bos grunniens) and Tibetan antelope(Pantholops hodgsonii, TA), which are endemic to the QTP, both have larger hearts, larger lungs, and elevated blood cell content, indicating that their blood supply system might undergo convergent evolution in response to high-altitude stress. However, it is still unclear whether these two species have undergone adaptive convergence at the genetic level. We used genomic data to detect possible examples of convergent evolution between yak and TA. Our results have provided clues that may be important for understanding high-altitude adaptations in animals.With the genomic data, we identified 7,950 single-copy orthologs in 7 species for further study. Through GO analysis, we found there were 660 accelerated GO terms specific in yak, and 568 accelerated GO terms specific in TA. Yak and TA shared 118 accelerated GO terms, many of which were related to the high-altitude adaptation, including “mitochondrial matrix”, “phospholipid metabolic process”, “glycolysis”, “ATP hydrolysis coupled proton transport”, “regulation of the force of heart contraction”, “sterol transporter activity”, “lipid catabolic process”, “response to cold”, “negative regulation of protein ubiquitination”, and “keratinocyte proliferation”. It indicated that genes related to energy metabolism, cold response, and energy metabolism might undergo convergent evolution between yak and TA, even though they had lineage-specific mechanisms for high-altitude adaptation. To further detect convergent genes between yak and TA, we developed a strict approach. Through ancestral site reconstruction, genome-wide scan, statistical significance test, site-wise log-likelihood support(SSLS) estimation, PCR amplification and sequencing, and phylogenetic analysis, we found only one gene, SOCS4, that showed significant parallel/convergent signals between yak and TA. Responding to the convergent evolution of blood supply system, SOCS4 is likely to be important for the survival of yak and TA.Through the genome-wide analysis between yak and TA, we have explored their potential genetic mechanisms for high-altitude adaptation. Our results have provided clues that may be important for understanding high-altitude adaptations in animals.