Better Together: Offspring Benefit from Siblings in Both the Absence and the Presence of Parents

AbstractFamily groups, ranging from simple to complexly structured, are widespread in the animal kingdom, with parent-offspring interactions in the form of parental care traditionally considered the primary driver of family life. However, recent considerations suggest that sibling cooperation might have facilitated the early evolution of social and family life. While the effects of isolated family interactions have been extensively studied, the intricate dynamics between different family interactions and their reciprocal impacts have gained little attention. Using a full-factorial social isolation experiment in the subsocial burying beetle <i>Nicrophorus vespilloides</i>, where we isolated offspring from siblings and/or parents, we showed that offspring benefited from the presence of both parents as well as siblings. The positive effects of siblings were evident in the absence and presence of parents, although they manifested differently. Without parents, growing alongside siblings resulted in higher larval mass at dispersal, perhaps due to advantages of collective feeding. With parents, having siblings accelerated early growth and increased survival, possibly due to higher begging activity, which may have influenced parental investment. Our results support the notion that beneficial sibling interactions are an important part of facultative family systems and may encourage offspring to stay in a family group.