Genetic sources of individual variation in parental care behavior

Consistent individual differences in behavior exist for many behavioral traits. Several evolutionary hypotheses regarding the maintenance of this variation have been proposed, but they all rest on the relatively untested question of whether this variation has a genetic basis and if so, exactly what genetic mechanisms may be involved. We tested for heritability and the effects of heterozygosity on two measures of parental care behavior (nestling provisioning rate and the likelihood of provisioning with large food items) in a population of wild house sparrows (Passer domesticus), where both behaviors display consistent individual differences across a wide range of contexts. We found no evidence of significant heritability in either measure of parental care behavior. However, in a subset of 46 female sparrows, the likelihood of bringing large food items to the nest, but not provisioning rate, was positively correlated with genetic heterozygosity estimated from 18 polymorphic microsatellite markers. Despite these findings, individual identity continued to explain a significant proportion of the variation in parental care behavior. Our results imply that while the effects of directional selection on traits associated with parental care may be limited in this population, genetic heterozygosity appears to play a role in the maintenance of phenotypic diversity in at least one aspect of parental care behavior.