Empirical evidence for multiple costs of begging in poison frog tadpoles

In recent decades, theoretical and empirical work has investigated the relative roles of costs and benefits in inhibiting excessive displays of begging to parents. Whether costs are important in maintaining reliability of offspring signals is still debated, in part because empirical evidence for costs is conflicting. Nearly 90% of empirical studies have focused on birds. Costs may differ between birds and other animal groups, but more information is needed about non-avian systems. In this study, we tested for evidence of costs of begging in an anuran, Oophaga pumilio, in which tadpoles vibrate vigorously against mother frogs to solicit nutritive eggs. First, we tested whether a realistic manipulation of begging effort affected tadpole growth over two weeks, and found evidence for such physiological costs. Second, we tested whether the presence of a natural predator would alter begging behavior. Tadpoles begged when hungry, but begged significantly less when both hungry and viewing a spider, suggesting that they have evolved to reduce potential costs of predation risk when begging. Thus, we demonstrate the first example of costs via both physiological expenditure and predation risk in a non-avian species. Unlike most birds which rear offspring in clutches, O. pumilio mothers rear tadpoles in individual sites, suggesting that in the absence of sibling effects, multiple costs of begging work concomitantly to prevent the expression and evolution of excessive or indiscriminate signaling. Future studies of begging from a comparative perspective will continue to augment our understanding of the mechanisms behind the evolution of parent-offspring communication.