Sex-specific effects of increased incubation demand on innate immunity in black guillemots.

Life-history theory predicts that there should be negative fitness consequences, in terms of future reproduction and survival, for parents with increased reproductive effort. We examined whether increased incubation demand affected innate immunity and body condition by performing a clutch-size manipulation experiment in black guillemots (Cepphus grylle). We found that plasma from males incubating experimentally enlarged clutches exhibited significantly reduced lysis titers compared with plasma from males incubating control clutches, while this was not observed in females. The increased incubation demand also impacted agglutination titers differently in males and females, although the effect of treatment was not significant in either sex. Among all birds, lysis titers increased and haptoglobin concentrations decreased from mid- to late incubation. Natural antibody-mediated agglutination titers and body condition were highly repeatable within the incubation bout and between years. This suggests that agglutination titers may serve as a reliable and resilient index of the immunological character of individuals in future studies. Overall, this study demonstrates that increased incubation demand impacts indices of innate immunity differently in males and females. The potential for different components of the immune system to be impacted sex-specifically should be considered in future studies linking immune function and life-history trade-offs.