MHC diversity associates with reproductive success in a bird species with biparental care

The selective pressure from pathogens on individuals can have direct consequences on reproduction. Genes from the major histocompatibility complex (MHC) are central to the vertebrate adaptive immune system and pathogen resistance. In species with biparental care, each sex has distinct reproductive roles and levels of investment, and due to a trade-off with immunity one can expect different selective regimes acting upon the MHC of each parent. Nonetheless, it remains to be addressed how couples combine each other’s variation at MHC loci to increase their breeding success. We used 23-years of data of a barn owl population (Tyto alba) to understand how MHC class Iα and IIβ functional divergence and supertypes of each parent influences clutch size and fledging success. We found several associations between fledging success and father’s MHC: a negative one with MHC-Iα divergence, and one negative and two positives with MHC-IIβ DAB2 supertypes. Fledging success was also influenced by interactions on two MHC-IIβ DAB1 supertypes on each parent. In contrast, clutch size was not influenced by MHC. Using cross-fostering data, we showed that lower MHC-Iα divergence might improve paternal care during incubation, while DAB2 supertypes seem to influence paternal care while rearing the chicks, possibly indicating a trade-off between individual quality and investment on reproduction. We speculate that, in this species, the effects of MHC are more advantageous during adult stage rather than during nestling stage. Future studies should account for different stages of reproduction and MHC classes, while also considering interactions between parents’ genetic diversity.