Characterization of major histocompatibility complex DRB diversity in the endemic South African antelope Damaliscus pygargus: a comparison in two subspecies with different demographic histories

Major histocompatibility complex (MHC) class II locus DRB was investigated by single-strand conformation polymorphism analysis (SSCP) and sequence ana lysis in the endemic South African antelope, Damaliscus pygargus, of which there are two subspecies. Greater polymorphism was found in the blesbok (D. p. phillipsi) subspecies (n = 44; 22 alleles) than in the bontebok (D. p. pygargus) subspecies (n = 45; 6 alleles). Erosion of allelic diversity in b ontebok was most likely the result of two severe bottleneck events caused b y hunting pressure and parasitic infection. A majority of the polymorphism observed was found within the peptide binding region (PBR) where dN/dS rati os were higher than for the non-PER region. This, and the apparent trans-sp ecies relationship among alleles in a bovid phylogeny, suggest the evolutio n of diversity by heterosis or frequency-dependent selection.