Cadmium does not affect post-hatching maternal care or early offspring development in earwigs

Anthropogenic pollution is steadily increasing and has a major impact on biodiversity. Chemical pollutants in particular affect many reproductive, physiological, and survival traits in a wide range of organisms. However, the effects on behavioral traits have been less studied, although they could have wide-ranging negative effects from the individual to the community level. Here, we attempted to fill this knowledge gap by investigating the effect of a common heavy metal pollutant, cadmium, on post-hatching maternal care and juvenile development in the European earwig Forficula auricularia. We fed 108 earwig families with five different cadmium concentrations (0, 12.5, 25, 50, and 100 mg.L-1), and measured ten parameters related to offspring care, non-care maternal behaviors, investment in maternal care and two parameters of offspring development (offspring weight gain and survival). Somewhat surprisingly, we found no effect of cadmium ingestion on any of the parameters measured, except for maternal self-grooming behavior. In particular, the ingestion of cadmium by group members did not result in an overall decrease in the expression of care by the contaminated mothers or in an overall higher level of care received by the contaminated offspring. By contrast, mothers fed the highest dose of cadmium showed an increase in self-grooming, probably due to the stress of toxic ingestion. Overall, our study raises questions about whether and how parent-offspring interactions can alter the negative effects of contaminated environments in social species. Heavy metal contamination does not necessarily shape parent-offspring interactions. We show that the ingestion of cadmium by earwig mothers and juveniles did not affect the expression of post-hatching maternal care. Nor did it did not affect the early development of offspring. It did, however, increase the expression of self-grooming by mothers. These findings raise fundamental questions about the underlying mechanisms that mediate the tolerance, resistance and/or detoxification of cadmium in this insect.