Love them all: mothers provide care to foreign eggs in the European earwig Forficula auricularia

The rejection of foreign individuals is considered a central parameter in the evolution of social life. Within family units, parents are typically thought to reject foreign offspring to ensure that their investment into care is directed towards their own descendants. Whereas selection for such kin bias is expected to be high when parental care is extended and involves numerous and energetically costly behaviours, it can be reduced when the acceptance of foreigners provide subsequent benefits to offspring and when alternative parental strategies limit the risk of clutch parasitism. In this study, we investigated the outcome of these conflicting selection pressures in the European earwig. Our results overall demonstrate that mothers do not eliminate foreign eggs, provide the same level of care to both foreign and own eggs (egg grooming, egg defense and maternal return) and pay the same costs of care in terms of weight loss and immunity when tending each type of eggs. We also show that for...