Meeting Abstract
Sexual selection theory has recently expanded our understanding of genetic quality to consider not only additive genetic effects on fitness but also non-additive genetic effects. In jawed vertebrates, a candidate gene family at which both additive and non-additive genetic effects on fitness has been demonstrated is the major histocompatibility complex (MHC). MHC genotype determines the range of pathogens to which an individual can respond, and thus, parasite-mediated selection at MHC often favors particular combinations of alleles (for example, heterozygote advantage). Provided that individuals are capable of assessing the MHC genotypes of potential mates, selection may thus favor non-random mating at MHC. We explored whether chemical cues in the preen oil of free-living song sparrows (Melospiza melodia) might convey information regarding MHC class II β genotype. Pairwise similarity in preen oil chemical composition predicted similarity at MHC, indicating a potential route for MHC signaling in songbirds. To investigate the potential for MHC-mediated mate choice, we compared MHC similarity of socially mated pairs of free-living song sparrows to random expectations. Contrary to our prediction of MHC-disassortative mating, social pairs were more similar at MHC than expected by chance. MHC-assortative mating in our system may reflect outbreeding avoidance or the maintenance of co-adapted gene complexes at immune or other loci. Collectively, our findings imply that song sparrows may use chemical cues to assess MHC similarity, but that such cues are used to achieve assortative, rather than disassortative, pairing.
