Disentangling the roles of social and individual effects on cadmium tolerance in the ant Temnothorax nylanderi

Abstract

Urbanization brings new pressures for individuals. Among them, trace elements, such as cadmium, are important stressors. A recent study highlights a weaker negative effect of cadmium on city colonies relative to their forest counterparts in the ant Temnothorax nylanderi. Here, we aim to test whether the better tolerance of city colonies in this species results from a better ability of workers to rear larvae despite stressful conditions and/or a better ability of larvae to develop properly despite stressful conditions. We performed a cross-fostering experiment of workers and larvae from city and forest colonies, in common garden conditions in the laboratory. Colonies were fed using cadmium-enriched or cadmium-free food for 2 months, and we measured four life-history traits. As expected, cadmium had a negative impact on all traits. Unexpectedly, we did not observe a better tolerance of city colonies to cadmium, contrary to our previous study, which prevented us from disentangling the respective contributions of workers and larvae to cadmium tolerance. Interestingly, forest colonies seemed to be of better quality in our laboratory conditions. Finally, colony size increased adult survival, but only in the absence of cadmium, suggesting that social buffering could collapse with strong external disturbances.

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

“…Cadmium, a highly toxic and diffusible element in the environment, is commonly known to have negative effects on numerous life-history traits in animals, such as development, survival, immunity, fecundity and fertility (e.g. Bryan et al, 1995;Cervera et al, 2004;Honorio et al, 2021;Jacquier et al, 2020;Malakar et al, 2009;Nanda & Firdaus, 2022). In this study, we used the European earwig, to test, for the first time, its effects on egg production and maternal egg care -a major fitness-related social behavior occuring in a wide range of animals (Meunier et al, 2022).…”

“…The consumption of this heavy metal entails many physiological and behavioral changes in various studied organisms. Physiological changes include, for instance, reduced growth in bluegills (Bryan, Atchison, & Sandheinrich, 1995), compromised growth and survival in grasshoppers (Malakar, Ganguly, & Haldar, 2009), and impaired growth, survival and fecundity in ants (Honorio, Jacquier, Doums, & Molet, 2021;Jacquier et al, 2020). Conversely, the behavioral changes include effects on cognition in humans (Gustin, Tofail, Vahter, & Kippler, 2018;Shao & Zhu, 2020), on locomotion and reproduction in Drosophila (Nanda & Firdaus, 2022), on aggressivity in rats (Arito, Sudo, & Suzuki, 1981) and on the formation of dominance hierarchies in trouts (Sloman et al, 2003).…”

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

“…Cadmium is a highly toxic and diffusible element in the environment that is known to affect the survival, reproduction and physiology of many species (e.g. Cervera et al 2004;Malakar et al 2009;Li et al 2018;Luo et al 2020;Honorio et al 2021). However, our study reveals that cadmium ingestion by earwig mothers and juveniles has only limited effects on the expression of maternal care, non-care behaviours and other life-history traits measured during the 14 days of parent-offspring interactions.…”

“…Apart from self-grooming, our data shows that cadmium consumption did not affect any other trait measured in mothers and juveniles during the 14 days following egg hatching. This is surprising because cadmium intake typically has negative effects on a wide range of traits, from survival to reproduction and development, in taxa from insects to mammals (Arito et al 1981;Cervera et al 2004;Malakar et al 2009;Li et al 2018;Jacquier et al 2020 Sep 30;Luo et al 2020;Honorio et al 2021;Nanda and Firdaus 2022). Even more surprising, developing nymphs did not suffer increased mortality following cadmium ingestion.…”

“…A growing number of studies show that cadmium ingestion can affect the physiology, development and reproduction of several species (e.g. Cervera et al 2004;Malakar et al 2009;Li et al 2018;Luo et al 2020;Honorio et al 2021). However, its effects on behaviour, and especially parental care, are still poorly understood and are sometimes contradictory.…”