Joël MEUNIER

I am delighted to see our research on earwigs featured in the Knowable magazine. There's a nice overview of the fascinating biology of this insect, our recent results, and behind-the-scenes stories from me and colleagues. A very nice piece of work!

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https://knowablemagazine.org/content/article/living-world/2024/social-life-of-earwigs

We tested whether parental care mitigates the impact of cold and heat waves on eggs and juveniles in the European earwig. We exposed mothers and their eggs to three-day thermal waves of 3°C, 10°C (control), 17°C or 24°C, both 15 and 30 days after oviposition. We then measured four maternal care behaviors, maternal weight variation, as well as eggs’ developmental time, survival, and hatching rate. In the resulting juveniles, we measured weight, developmental time, thermal resistance, and the expression of six heat stress and immunity genes. We found that thermal waves reduced maternal care and induced maternal weight gain. High temperatures also decreased egg hatching success, accelerated egg and nymph development, reduced the upper thermal limit of juveniles and decreased the expression of a heat shock protein (Hsp68), while other traits remained unaffected. Overall, this study suggests that species with maternal care do not necessarily have access to effective thermal protection and may not be better adapted to climate change. This study marks the first collaboration with Irene Villalta, more results to come ...

For the environmental week in Veigné, France, I had the pleasure of giving a talk to a large general audience about the secret life of earwigs. It was such a fun and engaging experience, with many familiar faces in the crowd. I truly love sharing this kind of knowledge, and it was a wonderful evening!

We tested whether insect parental care can enhance offspring survival against infections beyond the egg-laying stage. Using European earwigs, we challenged mothers with dead bacteria and later tested the survival of both the mothers and their adult offspring after a new exposure to live bacteria. We found that mothers who were immune-challenged after laying eggs, and their offspring, had higher survival rates. However, this increased survival was due to the physical wounding of the mothers, not their exposure to the dead bacteria. The findings suggest a novel benefit of post-egg-laying parental care in insects, highlighting the role of social immunity in the evolution of family life. This study is based on the work of Manon Boucicot, a Masters student. It is also the first publication from the collaboration with the EBI laboratory in Poitiers. 

We investigated the impact of molting and maternal care on the microbiome of the European earwig. Using 16S rRNA metabarcoding to analyze the prokaryotic fraction of the core microbiome, we showed that microbiome diversity changed non-linearly during earwig development, with notable shifts occurring between developmental stages rather than during molting. Additionally, we found that maternal care influenced the microbiome of both juveniles and adults, even when the last maternal contact occurred two months prior to adulthood. These findings offer new insights into the stability of the prokaryotic microbiome in hemimetabolous insects and challenge the role of maternal care in microbiome acquisition in species with facultative maternal behavior. This study advances our understanding of microbiome dynamics in relation to developmental processes and maternal care. This is the second study of MC Cheutin's postdoctoral project funded by the ANR MicroSoc.

Many of us had the pleasure of attending the IUSSI European meeting in Lausanne this year. It was absolutely brilliant! As well as presenting our latest data on the social life of earwigs to colleagues from all over the world, we were lucky enough to meet former members of the group who now work from Finland, Germany and other French cities. It was fantastic to catch up with them and see what they've all become. It was also an incredible opportunity to meet some brilliant colleagues and think about new projects and collaborations. Hopefully some new earwig research will come out of this meeting. Well done to the organisers!

In this review, we give a detailed overview of what we know about the European earwig and explain why it could be a fantastic model system for studying social evolution. After outlining (1) its life cycle and (2) its multiple forms of sociality, we explain how this species advances our knowledge of (3) the interplay between social conflict and cooperation in maintaining facultative social life, (4) the role of pathogens and symbionts in the transition between solitary and social life, (5) the impact of anthropogenic change on social evolution, and (6) the chemical, hormonal and genetic regulation of facultative social behaviour. I am very proud of this review, which was a collaborative effort between many students and colleagues working on earwigs. Have a good reading!

In this study, we tested the effects of sublethal exposure to a glyphosate-based herbicide (Roundup©) on the behaviour and immunity of male European earwigs from six natural populations. Overall, we found that exposure slightly reduced locomotor activity in males, but had no effect on any of the other traits measured. All these results were consistent across the six populations tested. These results, together with our previous findings with other pesticides and chemical pollutants, highlight the surprising resilience of the European earwig to chemical pollution and raise questions about the potential detoxification mechanisms at play in this species. This study is the first part of Laura's PhD project. Congratulations to her! It was financed by the ECOPHYTO national program and the Region Centre-Val de Loire.

Male weapons are large, extravagant structures that enhance fighting ability and reproductive success. In European earwigs, males have forceps-like cerci that vary in size within populations. We tested whether forceps length is associated with six behavioural and physiological traits by sampling hundreds of males from two populations and selecting 60 males with the longest and shortest forceps from each. We measured locomotor performance, boldness, aggregation behaviour, survival under harsh conditions, sperm storage, and survival after pathogen exposure. Contrary to our predictions, we found no association between forceps length and the traits measured, consistent across both populations. These results challenge our understanding of the function and quality signal of forceps length in earwigs and raise questions about the evolutionary drivers maintaining weapon size diversity. This study is the result of Sam's work while she was in our group as part of her international student exchange between France and Canada. 

It was a great pleasure to attend this meeting in Germany. It was full of bright and enthusiastic graduate students in evolutionary biology. I enjoyed listening to their talks and discussing their results and future projects. It was also a privilege to present our results on earwig family life and see the excitement in their eyes about our latest discoveries. Thanks to Max, Taina and Sandra for inviting me!