Parasite load and MHC diversity in undisturbed and agriculturally modified habitats of the ornate dragon lizard

MHC gene polymorphism is thought to be driven by host-parasite coevolution, but the evidence for an association between the selective pressure from parasites and the number of MHC alleles segregating in a population is scarce and inconsistent. Here, we characterized MHC class I polymorphism in a lizard whose habitat preferences (rock outcrops) lead to the formation of well-defined and stable populations. We investigated the association between the load of ticks, which were used as a proxy for the load of pathogens they transmit, and MHC class I polymorphism across populations in two types of habitat: undisturbed reserves and agricultural land. We hypothesized that the association would be positive across undisturbed reserve populations, but across fragmented agricultural land populations the relationship would be distorted by the loss of MHC variation due to drift. After controlling for habitat, MHC diversity was not associated with tick number, and the habitats did not differ in this r...