SEQUENCE VARIATION AT THE MAJOR HISTOCOMPATIBILITY COMPLEX LOCUS DQ-BETA IN BELUGA WHALES (DELPHINAPTERUS-LEUCAS)

Genetic variation at the Major Histocompatibility Complex locus DQ bet a was analyzed in 233 beluga whales (Delphinapterus leucas) from seven populations: St. Lawrence Estuary, eastern Beaufort Sea, eastern Chuk chi Sea, western Hudson Bay, eastern Hudson Bay, southeastern Baffin I sland, and High Arctic and in 12 narwhals (Monodon monoceros) sympatri c with the High Arctic beluga population. Variation was assessed by am plification of the exon coding for the peptide binding region via the polymerase chain reaction, followed by either cloning and DNA sequenci ng or single-stranded conformation polymorphism analysis. Five alleles were found across the beluga populations and one in the narwhal. Pair wise comparisons of these alleles showed a 5:1 ratio of nonsynonymous to synonymous substitutions per site leading to eight amino acid diffe rences, five of which were nonconservative substitutions, centered aro und positions previously shown to be important for peptide binding. Al though the amount of allelic variation is low when compared with terre strial mammals, the nature of the substitutions in the peptide binding sites indicates an important role for the DQ beta locus in the cellul ar immune response of beluga whales. Comparisons of allele frequencies among populations show the High Arctic population to be different (P less than or equal to .005) from the other beluga populations surveyed . In these other populations an allele, Dele-DQ beta0101-2, was found in 98% ofthe animals, while in the High Arctic it was found in only 5 2% ofthe animals. Two other alleles were found at high frequencies in the High Arctic population, one being very similar to the single allel e found in narwhal.