MAJOR HISTOCOMPATIBILITY COMPLEX I POLYMORPHISM IN A CETACEAN: THE GRAY WHALE (ESCHRICHTIUS ROBUSTUS)

Vertebrate Major Histocompatibility Complex‐I (Mbc‐I) proteins bind and display self and foreign peptides on the cell surface. Mbc‐I polymorphism is considered critical for eliciting immune responses to a diversity of antigens, and thus, for the health and conservation of a species. Based on restriction fragment length polymorphism it was concluded that whales generally have low Mbc‐I polymorphism. This was attributed to the weak pathogenic pressure in aquatic habitats. Since gray whales' habits might favor their encounter with diverse pathogens, resulting in selection pressures for Mbc variability, we searched for functional polymorphism of gray whale's Mbc‐I exon 2 sequences that encode the α‐1 protein domain of the antigen‐binding region. We sequenced twelve Mbc‐I exon 2 clones from each of seven gray whales. Most obtained sequences were similar to functional artiodactyl sequences, and their reconstructed phylogeny consistently showed three whale Mbc‐I exon 2 sequence clusters (A, B, and C). Sequences within a given cluster and from distinct clusters, showed a greater number of non‐synonymous than synonymous substitutions, that commonly shifted the physiochemical properties of the involved residue, suggesting the existence of a diverse repertoire of Mbc‐I antigen recognition sites in gray whales, and that selection maintains gray whale's Mbc‐I allelic diversity.