AbstractMHC genes are one of the most polymorphic gene clusters in vertebrates and play an essential role in adaptive immunity. There is evidence that sexual selection also plays a role in maintaining MHC diversity, but the specific mechanisms are controversial. In this study, we investigate evidence for non-random MHC-dependent mating patterns in a free-living population of Soay sheep. Using a large number of sheep diplotyped at the MHC class IIa region and genome-wide SNPs, together with field observations of consorts, we found sexual selection against one of eight haplotypes, C, in males at the pre-copulatory stage and sexual selection on female MHC heterozygosity acting in opposition directions at the pre- and post-copulatory stages. We also found disassortative mating at the post-copulatory stage, along with strong evidence of inbreeding avoidance at both stages. However, results from generalized linear mixed models suggest that the pattern of MHC-dependent disassortative mating could be a by-product of inbreeding avoidance. These results suggest that there is selection on the MHC at the pre- and post-copulatory stages, but that apparent disassortative mating with respect to the MHC may be driven by inbreeding avoidance.
An investigation of MHC-dependent sexual selection in a free-living population of sheep