Association between sexually selected traits and allelic distance in two unlinked MHC II loci in white-tailed deer ( Odocoileus virginianus )

Body size and secondary sexual characteristics are drivers of male reproductive success among polygynous species. A gene complex found to be associated with morphology in several species is the major histocompatibility complex (MHC). However, while several studies have found that greater MHC diversity is associated with larger body size and secondary sexual characteristics, other studies have demonstrated that maximal MHC diversity is not always optimal for the individual’s fitness. This study tested if MHC diversity, measured as pairwise allelic distances at each of two unlinked MHC II loci (exon 2 for the classical antigen-binding protein MHC-DRB and exon 2 for the accessory protein MHC-DOB), was associated with body size (male and female) or antler size in a semi-wild enclosed population of white-tailed deer (Odocoileus virginianus). After accounting for the effect of age on body and antler size, we used residual analysis to assess whether MHC allelic distances explained any of the remaining variation in body and antler size. While we found no associations between physical characteristics and MHC-DRB, we found that both male body and antler size were associated with MHC-DOB nucleotide allelic distances. Specifically, we found a quadratic relationship between MHC-DOB and male body size, where body size peaked at moderate MHC-DOB nucleotide allelic distance. However, we found a positive linear association between MHC-DOB nucleotide allelic distances and antler size. Neither MHC-DRB nor MHC-DOB influenced female body size, even though the average allelic distances of males and females were not significantly different. Our results suggest that MHC-DOB, or a gene genetically linked to this locus, may influence male morphological characteristics in white-tailed deer.