Effects of cadmium ingestion on reproduction and maternal egg care in the European earwig

Abstract

A growing number of studies show that anthropization can alter the behaviour, survival, physiology, cognition and reproduction of many animal species. However, its impact on parental care, a common behaviour where even subtle changes can have dramatic effects on the viability of future generations and thereby jeopardize population dynamics, remains surprisingly unclear. Here, we studied the effects of exposure to cadmium, a highly toxic chemical pollutant widely distributed in the trophic chain, on egg production and maternal egg care in the European earwig, Forficula auricularia . We fed 200 females with food containing cadmium at five different concentrations for several weeks, and then quantified the number of eggs produced, the expression of six forms of egg care and three forms of noncare behaviours, as well as maternal survival and egg development. In contrast to most results reported in other animal species, we found no evidence that ingestion of even substantial doses of cadmium affects egg production or maternal egg care in the form of grooming, antennation, displacement, gathering, defence or retrieval. Moreover, it neither affected maternal exploration, inactivity or self-grooming behaviours, nor egg development time, hatching rate or juvenile weight. Overall, these results reveal that egg care is resilient to environmental cadmium pollution in earwigs and suggest that females possess efficient and fast-acting physiological processes that help them reduce their sensitivity to heavy metal contamination. More generally, our findings may suggest that selection pressures associated with the necessity to express egg care has directly or indirectly selected for higher resistance/tolerance against certain chemical pollution, and thus that species with parental care could be more resilient in the face of increasing levels of anthropogenic pollution. • Egg care is an essential behaviour to ensure the viability of future generations. • Cadmium is highly toxic to organisms and affects numerous fitness-related traits. • We tested the effects of cadmium on egg care and reproduction in earwig females. • We found that egg care and female reproduction were independent of cadmium exposure. • The critical importance of egg care could explain the robustness of this behaviour.