Data from: When earwig mothers do not care to share: parent-offspring competition and the evolution of family life

1. Kin competition often reduces – and sometimes entirely negates – the benefits of cooperation among relatives, and hence is often regarded as central process in social evolution. Surprisingly, however, our understanding of the role of kin competition in the evolution of family life remains fragmentary, despite the close scrutiny it received in studies on sibling rivarly. This is because much less attention has been given to local competition between parents and their offspring, and its potential impact on the early evolution of parental care and family life. 2. Here, we examined mother-offspring competition over food access in the European earwig Forficula auricularia, an insect with facultative family life. Specifically, we (i) raised earwig offspring under food limitation either together with or without their mother, and then (ii) tested whether and how the – potentially competitive – weight gains of mothers and offspring during family life affected the offsprings’ survival rate and morphology, or the future reproductive investment of their mother. 3. In line with a mother-offspring competition over food access, we showed that high maternal weight gains during family life reduced the survival prospects of maternally tended offspring, while they increased maternal investment into second clutch production (but not the body size of the surviving offspring). Conversely, high offspring weight gains generally increased the offsprings’ survival, particularly when they were together with their mother. Intriguingly, mothers that had exhibited a low initial weight showed especially high weight gains. 4. Overall, our results demonstrate that maternal presence under food restriction triggered a local competition between mothers and their offspring. This competition limited offspring survival, but allowed mothers to increase their investment into future reproduction and/or to maintain their current body condition. On a general level, our findings reveal that local competition between parents and their offspring can counteract the benefits of (facultative) parental care, and may thus impede the evolution of family life in resource-poor environments