AFRICAN BUFFALO MAINTAIN HIGH GENETIC DIVERSITY IN THE MAJOR HISTOCOMPATIBILITY COMPLEX IN SPITE OF HISTORICALLY KNOWN POPULATION BOTTLENECKS

Historical population collapses caused by rinderpest epidemics are hyp othesized to have resulted in notable genetic losses in populations of the African buffalo. Polymorphism in the major histocompatibity compl ex (MHC) DRB3 gene was probed by means of restriction analysis of the sequence encoding the peptide-binding region. Nucleotide substitution patterns agreed with a positive selection acting on this fitness-relev ant locus. Buffalo populations from four National Parks, situated in e astern and southern Africa, each revealed a surprisingly high allelic diversity. Current high levels of heterozygosity may be reconciled wit h historical bottlenecks by assuming that local extinctions were follo wed by fast recolonization, in accordance with the high dispersive cap abilities of buffalo. The specific amplification of DRB3 alleles also enabled the assignment of individual genotypes. For each population sa mple a deficiency in the expected number of heterozygous animals was f ound. As overdominant selection on the MHC is predicted to yield an ex cess of heterozygous individuals, this may not be a locus-specific eff ect. Several other explanations are discussed, of which increased homo zygosity caused by nonrandom mating of buffalo in populations seems th e most probable.