Lifetime fitness benefits of short-distance dispersal and low costs of inbreeding drive inbreeding tolerance in an avian cooperative breeder

Breeding with relatives often decreases individual fitness but can be mitigated via inbreeding avoidance mechanisms such as dispersal, mate-switching, and kin avoidance. Disentangling the effects of multiple mechanisms is challenging without detailed individual-level data and incomplete without considering all life stages. We leveraged 32 years of data from a population of Florida Scrub-Jays ( Aphelocoma coerulescens ) to investigate how dispersal and mate choice contribute to inbreeding risk across individuals’ lifetimes and quantify the associated fitness outcomes. We find that when mating is random, inbreeding is two-fold higher when dispersal is limited, but adding sex-biased dispersal significantly reduces inbreeding risk. Limited movement away from the breeding territory for later pairings (site fidelity) contributes more to higher-than-expected levels of inbreeding than limited natal dispersal. Within observed dispersal constraints, however, inbreeding is lower than expected under random mating, suggesting Florida Scrub-Jays actively avoid mating with relatives, especially first-order kin. Finally, males paired with close relatives and females who move farther for later pairings experience equivalently lower lifetime reproductive success. Breeders who move farther for first pairings have lower survival. Overall, our results show how variation in fitness tradeoffs and mate choice behavior across life stages affects inbreeding in a long-lived, social species.