Lifetime fitness benefits of breeding site fidelity and low costs of inbreeding permit inbreeding tolerance in an avian cooperative breeder

Inbreeding, or breeding with close relatives, often decreases individual fitness, but mate choice can increase inbreeding risk in some species. Inbreeding is more likely in species with limited dispersal, such as cooperative breeders, where offspring frequently breed close to home. We leverage 32 years of data from a population of Florida Scrub-Jays (Aphelocoma coerulescens), an avian cooperative breeder, to investigate whether mate choice, and its lifetime fitness outcomes, affects inbreeding tolerance. We find that both sexes show shorter dispersal distances than expected under random mating. While female-biased natal dispersal mitigates inbreeding risk to some extent, limited movement away from the breeding territory by both sexes for later pairings (following mate death or divorce) results in higher relatedness between mates than expected under random mating. Males paired with close relatives and females who move longer distances experience equivalently reduced lifetime reproductive success (LRS). Moreover, breeders who move farther for first pairings experience reduced survival likelihood and consequently reduced LRS. Fitness benefits of short-distance dispersal and relatively low fitness costs of inbreeding thus permit inbreeding tolerance in Florida Scrub-Jays. Understanding how and why mate choice contributes to inbreeding is crucial for informed conservation of endangered species like the Florida Scrub-Jay.