Asynchronous hatching in burying beetles: a test of the peak load reduction hypothesis

The evolution of asynchronous hatching is a central yet controversial issue in evolutionary ecology and animal behaviour. Although asynchronous hatching has a widespread taxonomic distribution, past research has focused almost exclusively on altricial birds. We tested the peak load reduction hypothesis for the evolution of asynchronous hatching in the burying beetle Nicrophorus vespilloides, an insect in which parents provide their offspring with food after hatching. This hypothesis posits that caring parents benefit from asynchronous hatching because it reduces the parent's maximum workload during the peak in the offspring's demand for food. To test this hypothesis, we established three types of broods, synchronous, asynchronous and highly asynchronous, with a hatching span of 0, 24 and 48 h, respectively, and monitored effects on brood demand and female parental care. As expected, there were sharp peaks in both brood demand and female food provisioning, and the peak in brood demand decreased as a function of increasing levels of asynchronous hatching. However, in contrast to what we expected, the peak in female food provisioning was similar regardless of the level of asynchronous hatching, and offspring survival was substantially lower in highly asynchronous broods than in synchronous or asynchronous broods. We conclude that our results provide no overall support for the peak load reduction hypothesis. Further experiments are needed to establish the adaptive benefits of asynchronous hatching in this species.