Joël MEUNIER

Maternal egg care is generally considered to be ubiquitous among the 1,700 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 demonstrated for the first time that Forficula pubescens mothers 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 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. This manuscript is based on the Master project of Nicolas Mouret. 

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. We fed 200 females with food containing cadmium for several weeks and then quantified the number of eggs produced, the expression of egg care and non-care 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 any of the measured traits. This suggests that egg care is resilient to environmental cadmium pollution in earwigs and 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 have selected for higher resistance/tolerance against certain chemical pollutions, and thus that species with parental care could be more resilient in the face of increasing levels of anthropogenic pollution. This manuscript is the first one based on the ATER project of Romain Honorio 

We tested a new hypothesis suggesting that the need for juveniles to access sibling interactions may encourage juveniles to remain in a family group, thereby consolidating the early stages of family life evolution when parental care is facultative. We found that isolated earwig nymphs reached adulthood more quickly and that these adults were overall larger but showed an impaired aggregation behaviour compared to nymphs raised with siblings or with siblings and their mother. By contrast, sibling deprivation did not affect offspring survival, male forceps length and three other behaviours in adults (boldness, general activity, and exploration). Altogether, our findings suggest that the potential benefits of sibling interactions measured in this study play a minor role in the maintenance of earwig family life. They also emphasize the need to study the evolutionary drivers of family life in species where all members can switch from family to solitary life - a scenario that probably prevailed in the early evolution of sociality.  This manuscript is the 7th and last manuscript based on Sophie Van Meyel's PhD thesis. 

We had a great time hosting Nicolas, Manon, and Sarah during their internship. Their projects on hormonal regulation of maternal care, immune priming, and the effects of heavy metal pollution on earwig behaviours and morphology provided fantastic data that we hope you will read about very soon. It's sad to let you go, but travelling the world and experiencing new things in other labs or other paths is what brilliant students do! We have been lucky to have you around. We wish you the best in your future careers and hope you will always remember how earwigs rock!

In this study, we tested the effect of pyriproxyfen exposure (an insect growth regulator) on maternal care in the European earwig. We exposed 424 females at doses either 10 times lower, equivalent or 10 times higher than normal application rates in French orchards and then measured the expression of ten forms of maternal care towards eggs and juveniles, six non-caring behaviours, eggs and juveniles development, metabolic reserves in mothers at egg hatching and females’ production of a terminal clutch. Our results revealed no effect of pyriproxyfen on maternal care and non-care behaviours, eggs and juveniles development, quantities of lipids, proteins and glycogen in mothers at egg hatching, and the production of a future clutch. Overall, these findings suggest that the maximal doses of pyriproxyfen authorized in French orchards are likely to have limited effects on the short- and long-term maintenance of populations of the European earwig and raise fundamental questions about the nature of the link between the juvenile hormone and parental care in insects. This study has been financed by the Region Centre Val de Loire (project DisruptCare) and the National program Ecophyto 2+ (project BioIndicFin).

It was a great pleasure to have Célia on board. Her pilot results suggest that the ingestion of Cadmium during nymphs development impacts certain behavioural traits in adult earwigs. We wish you all the best for your academic future, Célia! 

Depositing eggs in an area with adequate temperature is often crucial for mothers and their offspring, as the eggs are immobile and therefore cannot avoid exposure to suboptimal temperatures. Here, we show that earwig females select oviposition sites according to temperature, and can move their eggs to reach warmer temperatures that are necessary to ensure egg hatching. Overall, this study sheds light on a new post-oviposition strategy in female insects that overwinter with their eggs for coping with temperature changes. It also reveals that egg care and/or egg transport do not prevent behavioural thermoregulation via oviposition site selection and highlights the diversity of behaviours that insects can adopt to enhance their tolerance to global climate change. This study is another product of the fruitful collaboration with our Canadian friend and collaborator JC Tourneur.

We continue in 2022 by welcoming a new student to the team. During her 7-week internship, Célia will study whether long-term exposure to heavy metals affects adult personality in the European earwig. This project will be carried out in collaboration with Charlotte Lécureuil and Romain Honorio.

We are opening a PhD position to study the link between exposure to pesticides and parental care in earwigs. If you have a strong background in insects physiology, evolutionary biology and/or behavioural ecology. If you show an interest in the development of new molecular tools. If you are motivated, energetic, independent and a good team player: you should definitively apply!! (see link above). The starting date is September 2022, and the deadline for application is 27 April 2022.

It was a great pleasure to host Pauline during her 2 months internship. She investigated the effects of pollutants on social behaviour in earwigs and was involved in many other projects during her stay. Pauline was motivated, industrious, curious and always in a good mood. We wish you all the best for your future, Pauline!

Our chapter has been published in a book overall entitled "reproductive strategies in insects". It is edited by Omkar and Geetanjali Mishra and published by CRC Press / Taylor and Francis (link). In this chapter, we detail the astounding diversity of parental care in insects. We start by presenting forms of parental care that occur before oviposition, then move to forms occurring between oviposition and egg hatching and conclude with forms of post-hatching parental care occurring before and/or after nutritional independence. This comprehensive review demonstrates overall that insects represent a perfect example of the diversity of parental care that can be found in animals, and thus emphasizes why they are excellent biological models for improving our general understanding of its evolution, diversification and underlying physiological and genetic mechanisms. Writing this chapter (and surviving to its editorial process) was a very fun and instructive experience with my colleagues and friends Jos Karmer (University of Zurich, CH) and Maximilian Körner (University of Bayreuth, GE).

We are more than happy to start 2022 by welcoming a fantastic group of students and collaborators!! Manon, Pauline and Nicolas are Masters students and will be studying the link between immune priming and maternal care, the hormonal regulation of maternal care and the effect of heavy metal pollution on maternal care in the European earwig, respectively. These projects will be carried out in collaboration with Charlotte Lécureuil and Romain Honorio (University of Tours), and with Christine Bracquart Varnier, Julien Verdon and Alexandre Crepin (University of Poitiers). Marie-Charlotte is a post-doc funded by the ANR Microsoc project and will study the gut microbiota of the European earwig and its effect on social evolution.