The evolution of parental care in shorebirds: life histories, ecology, and sexual selection

Abstract

Parental care is expected to evolve according to a trade-off between the benefits of increased survival of offspring and costs of reduced survival and future reproduction of adults. Here we investigate the components of this life-history trade-off in shorebirds (Charadriides, excluding Laroidea), an avian infraorder displaying an unusual diversity in extent of care by each sex. We show that evolutionary increases in the duration of care in one sex are associated with decreased care by the other. We found no evidence that various hypothesised benefits of care provide a general explanation for the duration of care by either or both sexes, although parental feeding of the young was too conservative for comparisons. Sexual dimorphism in body size had a similar relationship to parental care in both sexes: reductions in duration of care by either sex were matched by increases in the size of that sex relative to the other. Whereas this pattern could be explained by sexual selection in males, it was retained within socially monogamous females. Reduced care in males (but not in females) appears to have facilitated the evolution of greater migration distances. These results suggest that parental care has had different causes and consequences in each sex. Benefits of desertion due to sexual selection are more clearly demonstrable for males, whereas correlates of care are less clear for females.