MHC-II distance between parents predicts sex allocation decisions in a genetically monogamous bird

Abstract Theory predicts that parental heritable characteristics should shape sex allocation decisions when their effects on reproduction or survival are offspring sex-dependent. Numerous studies have questioned to what extent displayed by one of the parents matched theoretical expectations. This contrasts with handful investigated whether compatibility between could also trigger selective pressures for adjustments. We studied genetically monogamous black-legged kittiwake (Rissa tridactyla), where previous data revealed female chicks suffered higher fitness costs from low diversity at genes major histocompatibility complex (MHC) than male chicks. predicted, and found in our dataset, MHC-similar parents, producing MHC-diverse offspring, avoid production females. The relation MHC-distance (i.e. functional distinctness MHC alleles) was not linear, such MHC-dissimilar overproduced sons. Overall, results suggest flexibly adapt circumvent suboptimal pairing manipulating sex.