Divergent Cardiovascular Adaptations and Gene Regulation in High-Elevation Natives and Recent Colonizers of the Qinghai-Tibetan Plateau.

High elevation imposes unrelenting and unavoidable hypoxia on species inhabiting these environments, providing an excellent natural setting for studying convergent or divergent evolution. By integrating measures of phenotypic variation, gene regulation, and functional performance, our study demonstrates that recent colonizers of high-elevation environments exhibit fundamentally different cardiovascular changes compared to long-term natives of these environments. Through the studying of heart morphological phenotypes, we showed that recent colonizers exhibit signs of cardiac hypertrophy, reflected by increased relative heart mass (heart mass/body mass) and cardiomyocyte size compared to their low-elevation relatives. In contrast, native species show no signs of cardiac hypertrophy and instead have 3-fold higher capillary densities than the colonizers, a change that likely enhances tissue oxygen diffusing capacity in the former. Using phylogenetic principal component analysis to quantify multivariate trait divergence, we show that native species are similar in cardiovascular phenotype and underlying gene expression, but differ appreciably from recent colonizers. We further demonstrate, using a functional assay, that differential expression of two genes (IRS2 and AKT1) in a conserved regulatory pathway mediates cardiomyocyte hypertrophy, which could explain the observed variation in cardiomyocyte size between native species and recent colonizers. This regulatory basis of variation in cardiac phenotype involves the differential expression of genes in a cardiomyocyte hypertrophy pathway that is conserved across birds, humans and other mammals. Collectively, our study highlights that evolutionary history is a critical determinant of cardiovascular variation in high-elevation environments.