Amazon river dolphin polymorphism and population differentiation of MHC class II peptides

Inia, the Amazon River dolphin, inhabits the three major basins of northern South (Beni-Mamoré, Amazon and Orinoco). We analyzed class II DQB MHC gene peptide sequences in 60 dolphins from Bolivia (Beni-Mamoré), Peru (Amazon) and Colombia (Orinoco). Sixteen (16) peptide alleles were identified, generated by 17 polymorphic sites, most of them on the peptide binding region (PBR) residues. Four of the alleles were the most frequent of all the populations and several private alleles for each basin were found. A high level of polymorphism in the class II gene was determined, similar to those reported for the Chinese river dolphins, such as the Baiji and the finless porpoise. This polymorphism could be an adaptive response to the high level of pathogens in freshwater.