Elucidating the genomic and molecular underpinnings of high-altitude adaptation in andean waterfowl species

Hypoxia (or low O2) is one selective pressure that stimulates a similar physiological response across metazoans allowing organisms to match O2 supply and demand. During reduced O2 supply, changes in gene expression are mediated by transcription factors known as Hypoxia-Inducible Factors (HIF), which have been shown to play a key role in cellular responses to low O2 tension in a variety of organisms. Here we test whether variation in 26 genes in the HIF signaling pathway are associated with high-altitude and corresponding O2 availability in several duck species that colonized the Andes from ancestral low-altitude habitats in South America: speckled teal (Anas flavirostris) and yellow-billed pintail (Anas georgica). Ultimately, we found strong support for both convergent and parallel evolution at different taxonomic levels. Specifically, the same exonic regions in the same genes (EGLN1, EPAS1) exhibited sharply demarcated outliers with a high probability of directional selection in two high-altitude populations. In addition, between the high-altitude populations of speckled teal and yellow-billed pintail, there was evidence of strong molecular parallelism at the location of specific exons resulting in nonsynonymous changes in close proximity to protein domains associated with oxygen-driven protein stability and transactivation. Although the specific molecular mechanisms associated with these variants are currently unknown, previous work suggests that these variants are likely resulting in a blunted hypoxic response, potentially through hemoglobin and other downstream targets.