Major histocompatibility complex variation in the Arabian oryx

In the 1960s, the Arabian oryx was one of the most endangered species in th e world, extinct in the wild and surviving in only a few captive herds. The present day population of over 2000 descends from a small number of founde rs and may have restricted genetic variation for important adaptive genes. We have examined the amount of genetic variation for a class II gene in the major histocompatibility complex thought to be the most important genetic basis for pathogen resistance in vertebrates. We found three very divergent alleles, which on average, differed by 24 nucleotides and 15 amino acids i n the 236-bp fragment we examined. Using single-strand conformation polymor phism, we found that in a sample of 57 animals, the alleles were in Hardy-W einberg proportions, although one allele was found only in four heterozygou s individuals. The average heterozygosity for the 22 amino acid positions i nvolved in antigen binding was 0.165, three times as high as that for the 5 6 amino acids not involved with antigen binding. Because the three alleles have such divergent sequences, it is likely that they may recognize peptide s from quite different pathogens. As a result, maintenance of these variant s should be considered as a goal in the captive breeding program of the Ara bian oryx.