Is there a cost to larval begging in the burying beetle Nicrophorus vespilloides?

Offspring of many animals signal their nutritional needs using conspicuous begging displays. Theoretical models for the evolution of begging suggest that costly begging signals provide an evolutionarily stable resolution to parent-offspring conflict because they provide parents with honest information on offspring need. However, other models suggest that cost-free or low-cost begging can evolve because parents and offspring have overlapping interests. Empirical studies on birds provide mixed and ambiguous evidence for begging costs. Here, we examine begging costs in the burying beetle Nicrophorus vespilloides. Larval begging may incur a growth cost as in birds or an opportunity cost because larvae cannot beg for food and self-feed at the same time. We used a novel experimental design, in which we controlled begging through the presence or absence of a dead parent simultaneously as we controlled the opportunity to self-feed through the presence or absence of food. As intended, the presence of a dead parent stimulated larval begging, whereas larvae never begged when the dead parent was absent. However, the presence or absence of a dead parent had no effect on larval growth. Likewise, the interaction between the presence or absence of food and the presence or absence of a dead parent had no effect on growth. Thus, our study provides no evidence of either a growth cost or an opportunity cost of larval begging in N. vespilloides. The lack of evidence for any significant begging costs suggests that cost-free or low-cost begging could be more common than hitherto recognized.