MAJOR HISTOCOMPATIBILITY COMPLEX VARIATION ASSOCIATED WITH JUVENILE SURVIVAL AND PARASITE RESISTANCE IN A LARGE UNMANAGED UNGULATE POPULATION (OVIS-ARIES L.)

Antagonistic coevolution between hosts and parasites has been proposed as a mechanism maintaining genetic diversity in both host and parasit e populations, In particular, the high levels of genetic diversity wid ely observed at the major histocompatibility complex (MHC) of vertebra te hosts are consistent with the hypothesis of parasite-driven balanci ng selection acting to maintain MHC genetic diversity, To date, howeve r, empirical evidence in support of this hypothesis, especially from n atural populations, has been lacking, A large unmanaged population of Soay sheep (Ovis aries L.) is used to investigate associations between MHC variation, juvenile survival, and parasite resistance. We show in an unmanaged, nonhuman population that allelic variation within the M HC is significantly associated with differences in both juvenile survi val and resistance to intestinal nematodes, Certain MHC alleles are as sociated with low survivorship probabilities and high levels of parasi tism or vies versa, We conclude that parasites ape likely to play a ma jor role in the maintenance of MHC diversity In this population.