The evolution of ancestral and species-specific adaptations in snowfinches at the Qinghai-Tibet Plateau

Species in a shared environment tend to evolve similar adaptations under the influence of their phylogenetic context. Using snowfinches, a monophyletic group of passerine birds (Passeridae), we study the relative roles of ancestral and species-specific adaptations to an extreme high-elevation environment, the Qinghai-Tibet Plateau. Our ancestral trait reconstruction shows that the ancestral snowfinch occupied high elevations and had a larger body mass than most nonsnowfinches in Passeridae. Subsequently, this phenotypic adaptation diversified in the descendant species. By comparing high-quality genomes from representatives of the three phylogenetic lineages, we find that about 95% of genes under positive selection in the descendant species are different from those in the ancestor. Consistently, the biological functions enriched for these species differ from those of their ancestor to various degrees (semantic similarity values ranging from 0.27 to 0.5), suggesting that the three descendant species have evolved divergently from the initial adaptation in their common ancestor. Using a functional assay to a highly selective gene, DTL, we demonstrate that the nonsynonymous substitutions in the ancestor and descendant species have improved the repair capacity of ultraviolet-induced DNA damage. The repair kinetics of the DTL gene shows a twofold to fourfold variation across the ancestor and the descendants. Collectively, this study reveals an exceptional case of adaptive evolution to high-elevation environments, an evolutionary process with an initial adaptation in the common ancestor followed by adaptive diversification of the descendant species.

Automated summary

This study focuses on snowfinches as a monophyletic group of passerine birds to explore the evolution of species-specific adaptations in extreme high-elevation environments, especially the Qinghai-Tibet Plateau. The research reveals that about 95% of genes under positive selection in the descendant species differ from those in the ancestor, leading to differences in enriched biological functions among these species. The study also shows an exceptional case of adaptive evolution in high-elevation environments, indicating an initial adaptation in the common ancestor followed by adaptive diversification of the descendant species.