IgE receptor polymorphism predicts divergent, sex-specific inflammatory modes and fitness costs in a wild rodent

Sexual dimorphism is widespread in the animal kingdom, with males and females differing in their physiology, morphology and behaviour. However, relatively little is known about the importance of sex for the expression of genotype in natural populations, particularly in the context of health and disease. We combine data on genotype, immune gene expression, infection incidence and pedigree of individuals in a wild population of field voles (Microtus agrestis). We identify a polymorphism in the Immunoglobulin E (IgE) receptor with sexually dimorphic effects on immune phenotype, health and, ultimately, fitness. While males with the polymorphism upregulate their pro-inflammatory response with a detrimental effect on their reproductive success, females upregulate their anti-inflammatory response, increasing their risk of infection, but with no apparent reproductive cost. Our work demonstrates the potential for the same genetic difference to have profoundly different consequences for the health and fitness of males and females in natural populations.