Molecular genetic diversity and evolution at the MHC DQB locus in four species of pinnipeds

Variation was investigated at exon 2 (including part of the putative peptid e-binding region) of the class II major histocompatibility complex (MHC) DQ B locus for two congeneric phocid seal species and two congeneric otariid s eal species. Polymorphism in one phocid species, the southern elephant seal (Mirounga leonina), was comparable to that seen in human populations, whil e the other phocid, the northern elephant seal (Mirounga angustirostris), h as been through a severe population bottleneck and exhibited much less vari ation at this locus. A phylogenetic comparison of the four species was cons istent with the trans-specific pattern of evolution described for other tax a at this locus, and relative nonsynonymous and synonymous substitution rat es suggest the maintenance of polymorphisms by natural selection. A compari son of sequence patterns also suggested that some variation could have been generated through recombinational events, primarily within genera. These r esults suggest a pattern of evolution of the immune response in pinnipeds s imilar to that in terrestrial mammal species.