Major histocompatibility complex DRB genes and blood parasite loads in fragmented populations of the spotted suslik Spermophilus suslicus

Major histocompatibility complex (MHC) variability is believed to be maintained by balancing selection, whereby the major selective force is a wide range of pathogens interacting with their hosts. Pathogen-driven selection can be mediated through heterozygous advantage, frequency-dependent selection and/or fluctuating selection. There is growing evidence that MHC alleles are associated with resistance or susceptibility to infections among mammals, but for endangered populations such data are scarce. Here we investigated the associations between MHC class II DRB alleles and the load of blood parasites in fragmented populations of the endangered spotted suslik Spermophilus suslicus.Heterozygosity at DRB alleles did not affect parasite prevalence or infection intensity, but we found evidence that specific DRB alleles are related to infection by the most common of blood parasites infecting this species, Haembartonella sp. There was an interaction between the Spsu-DRB*03 allele and population in their effects on the prevalence and intensity of infection. In some populations the frequencies of DRB alleles deviated from Hardy–Weinberg equilibrium, suggesting that selection is acting on the MHC locus.Overall, our data suggest that MHC DRB is an important determinant of the parasite load in endangered spotted suslik populations.