The costs and benefits of maternal egg care in the earwig Forficula pubescens

Abstract

Maternal egg care is generally considered to be ubiquitous among the 1700 species of free-living Dermaptera. However, the forms, costs, and benefits of egg care have only been studied in a handful of species. In this study, we examined for the first time egg care in the earwig Forficula pubescens. Under standard laboratory conditions, we set up 94 families containing mothers with either no eggs, a reduced, normal or increased clutch size, or eggs without mother. We first demonstrate that F. pubescens mothers indeed express multiple forms of egg care including egg grooming, egg guarding, and active defences against predators, some of which vary with clutch size. However, maternal presence had contrasting effects on the eggs’ fate. On the one hand, it reduced the survival of eggs during their first 30 days of development, which suggests that mothers eat part of their clutch during egg development and, contrary to other Dermapterans, that abandoned eggs can resist fungal development. On the other hand, maternal presence was necessary to allow the remaining eggs to hatch on day 53, indicating that mothers enhance late embryonic development and/or facilitate the hatching process. Finally, our results did not shed light on the costs of egg care for mothers in terms of premature death, reduced expression of self-grooming, or increased weight loss. Overall, our study emphasizes that investigating the costs and benefits of egg care in poorly known species can provide novel insights into our understanding of the evolution of maternal care within and across animal taxa.