Lifetime fitness benefits of short-distance dispersal are associated with inbreeding tolerance despite multiple inbreeding avoidance mechanisms

Abstract

It is commonly assumed that mechanisms that reduce inbreeding, such as sex-biased dispersal or kin avoidance, are always adaptive. However, theoretical models predict that inbreeding avoidance evolves only when the relative costs of inbreeding are higher than the costs of inbreeding avoidance. We empirically tested this prediction with 32 years of data on Florida scrub-jays (Aphelocoma coerulescens), birds with short dispersal distances and multiple mating opportunities over their lifetimes. Using simulations, we showed that limited dispersal increases the inbreeding risk by at least two-fold, with a stronger effect at later life stages. Sex-biased dispersal reduces, but does not eliminate, this risk. Additionally, we found that the fitness costs of inbreeding are lower than those of dispersal in terms of lifetime reproductive success (LRS) and survival. Inbreeding is associated with substantially lower LRS only when mates are first-order kin. Accordingly, we found that the population shows a degree of inbreeding tolerance but, within their dispersal constraints, Florida scrub-jays actively avoid mating with first-order kin. Overall, our results empirically demonstrate the context-specific nature of inbreeding avoidance, with selection favoring limited dispersal despite costs of inbreeding and inbreeding avoidance via mate choice only when the relative fitness costs of inbreeding are particularly high.