More parental care leads to higher offspring fitness, but more carers do not: an experimental study in burying beetles

Animals have various forms of cooperation during breeding. The benefits of helping behaviour, such as raising the young of conspecifics, are well studied in cooperative breeding systems, where kin selection plays a role. However, for communal breeding, which consists of multiple, unrelated individuals with shared reproduction, such benefits and the impact of parental care remain poorly understood. Thus, in this study, the combined effects of communal breeding and parental care on reproductive success and offspring traits were investigated using burying beetles, Nicrophorus vespilloides, which is a species that breeds in pairs or communal groups and provides care for larvae during pre and posthatching. The reproductive shares in communal groups were also examined through parentage analysis. Single carcass was allocated to breeding groups of either two pairs (communal breeding) or one pair (pair breeding) of beetles, thereby manipulating the parental treatment by allowing larvae to be raised in the presence or absence of posthatching care (full care versus half-care) for both breeding groups and observing their reproduction and offspring performance. Communal breeding was expected to enhance offspring development compared with pair breeding because of more breeders increasing cooperative care for larger communal broods. Contrary to expectations, communal groups produced smaller offspring but the same brood sizes compared with pair-breeding groups. As predicted, the absence of posthatching care resulted in smaller offspring in both breeding groups, whereas its absence did not impose considerable cost in communal breeding compared with pair breeding. Dominants in communal groups accounted for most reproduction compared with subordinates, but dominants and subordinates produced substantially fewer larvae compared with pair-breeding females. Therefore, communal breeding results in higher costs than more benefits for reproduction and offspring fitness, where more breeders may not necessarily provide enhanced total parental care to the offspring of shared broods.