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

Various forms of cooperation during breeding are widespread within and across animal species. The benefits of helping behaviour, such as raising the young of other conspecifics, are well studied in cooperative breeding systems, where kin selection plays a role. However, for communal breeding consisting of multiple, unrelated individuals with shared reproduction, such benefits and the impact of parental care remain poorly understood. To fill this gap, we experimentally investigated the combined effects of communal breeding and parental care on reproductive success and offspring traits, and examined reproductive shares in communal groups through parentage analysis, using the burying beetles Nicrophorus vespilloides. These beetles can breed as pairs or together in communal groups and provide care to their larvae during the pre- and post-hatching periods. We subjected beetle individuals to communal or pair-breeding on a single carcass, manipulating the parental treatment by allowing larvae to be raised in the presence or absence of post-hatching care (full-care vs. half-care). We expect that communal breeding will result in enhanced benefits in offspring development compared to pair breeding, due to increased cooperative care towards all offspring. Contrary to our expectations, communal groups produced smaller offspring, but similar brood sizes compared to pair-breeding groups. However, the presence of post-hatching care resulted in larger offspring compared to the absence of post-hatching care. Dominants in communal groups accounted for most reproduction compared to subordinates, whereas they both produced substantially fewer larvae compared to pair-breeding females. Our study shows that communal breeding results in higher costs than benefits at the groups and individuals' levels for burying beetles, where more caring individuals may not necessarily offer enhanced parental care to each other's offspring.