MHC-DRB heterozygosity may increase subordinate but not alpha male siring success in white-faced capuchin monkeys (Cebus imitator).

The genes of the major histocompatibility complex (MHC) are vital to vertebrate immunity and may influence mate choice in several species. The extent to which the MHC influences female mate choice in primates remains poorly understood, and studies of MHC-based mate choice in platyrrhines are especially rare. White-faced capuchin monkeys (Cebus imitator) reside in multimale-multifemale groups where alpha males sire most of the offspring, but females related to the alpha male reproduce with subordinate males. In this study, we investigated the potential role of MHC genotypes, in the context of social dominance and relatedness, in determining which mating pairs produced offspring in wild white-faced capuchins in the Sector Santa Rosa, Área de Conservación Guanacaste, Costa Rica. We found that neither the social status nor the siring success of males was associated with their MHC metrics. Using mixed conditional logit models and generalized linear models, we found that MHC metrics did not predict the probability of siring offspring or being an alpha male. Alpha males that were distantly related to reproducing females were significantly more likely to sire offspring regardless of MHC genotype. However, we did find some evidence that subordinate males heterozygous at MHC loci sired significantly more offspring than homozygous subordinate males. Further, one-sided binomial simulations revealed that offspring were more frequently heterozygous at MHC loci than expected given the gene pool. We conclude that in this population, females related to the alpha may preferentially mate with MHC-diverse subordinate males, leading to increased probabilities of MHC-diverse offspring.