The Effect of Female Condition on Maternal Care in the European Earwig


Janine W. Y. Wong, Zoological Institute, Evolutionary Biology, University of Basel, Vesalgasse 1, 4051 Basel, Switzerland.


Parental care typically enhances offspring fitness at costs for tending parents. Asymmetries in genetic relatedness entail potential conflicts between parents and offspring over the duration and the amount of care. To understand how these conflicts are resolved evolutionarily, it is important to understand how individual condition affects offspring and parental behaviour and whether parents or offspring make active choices in their interactions. Condition effects on offspring have been broadly studied, but the effect of parental condition on parent–offspring interactions is less well understood, in particular in species where care is facultative and offspring have the option to beg for food from the parents or to self-forage. In this study, we carried out two experiments in the European earwig Forficula auricularia, a system where females provide facultative care, in which we manipulated female condition (through a high-food and low-food treatment) and the degree by which mothers and offspring could make active choices. In a first experiment, where female mobility was limited, female condition had no significant effect on the rate of offspring self-foraging, which increased with nymph age. In a second experiment, nymph access to food was limited and females in poor nutritional condition provided food to significantly fewer nymphs than high condition females. In both experiments, offspring attendance remained at a constantly high level and was independent of female condition even after experimental separation of females and offspring. Our results show that earwig nymphs do not use cues of female condition to adjust rates of self-foraging, that females control food provisioning depending on their own condition, and that females and nymphs share control over offspring attendance, a form of care not influenced by female condition.