Parent-offspring competition for food constrains parental care in communal carrion beetles

Abstract

Parents and offspring of many animals regularly share food resources, which may promote competition among kin for food and ultimately constrain the development of family life. We hypothesize that parent-juvenile competition for shared food is especially intense in communal systems, particularly those that exploit ephemeral resources (e.g. carrion), promoting early dispersal of adults from a shared resource and in this way constraining parental care. We tested this hypothesis in communal carrion beetles Necrodes littoralis (Staphylinidae), a species colonizing cadavers of large vertebrates that exhibit no post-hatching forms of parental care. By manipulating the number of adult beetles, the time they stay on food resources and the quality of that resources, we provide evidence that parent-juvenile competition for food on carrion has a constraining effect on parental care in communal carrion beetles. When we doubled the time spent by adult beetles on shared food, there was a clear negative effect on juvenile fitness, but doubling the number of the beetles had no significant effect. Therefore, parent-juvenile competition for shared food resources limits primarily the time adult communal beetles stay on carrion. By promoting earlier dispersal of adult beetles from a nesting site, this form of competition reduces the time window for potential adult-juvenile interactions, which makes post-hatching care virtually impossible to develop in these beetles. These findings highlight the importance of competitive adult-juvenile interactions in the large communal groups that use high-quality ephemeral resources.