CONICET | Buscador de Institutos y Recursos Humanos

Birds that inhabit highland environments tolerate hypoxia due to physiological and morphological adaptations. Even though mitochondrial genes participate in the cellular respiratory process, their role in the adaptation to hypoxia has been poorly studied and analyses are needed to establish general patterns of mitochondrial adaptation to high altitude. In this context, we studied the adaptation of COI to hypoxia. The choice of this gene is based on two main reasons: 1) it catalyzes the last reduction of oxygen in the electron transport chain, and 2) large-scale sequence libraries of a portion of this gene are available due to the Barcode of Life project. Over 22,000 sequences of the COI barcode region were retrieved from around 2,000 avian species from the American Continent. Using a complete phylogeny of the birds of the World we classified 155 pairs of sister species into highland-lowland, highland-highland, and lowland-lowland species pairs to compare their COI sequences. We found both more changes in amino acids and a higher proportion of sister species pairs with amino acid differences when at least one of the species of the pair was a highland species. We also analyzed the amino acids that differed between the species to establish their position in the protein and the effect of the change in their properties. Because the COI barcode region represents only a portion of this gene, we sequenced the complete gene for a reduced set of 28 sister species pairs. For these, we established the direction of the amino acid change between species and used protein modeling methods to assess the potential functional effect of these changes. This is the first large-scale analysis of mitochondrial adaptation to high altitude in any taxonomic group, and results suggest that the adaptation of COI to hypoxic highlands in birds is not generalized but idiosyncratic.