Surrounding pathogens shape maternal egg care but not egg production in the European earwig

Abstract

Pathogens are ubiquitous in nature and typically entail major fitness costs in their hosts. These costs can be particularly important when individuals exhibit poor immune defences, as it is often the case during early developmental stages. Hence, selection should favor parental strategies limiting the risks of pathogen exposure and infection in their offspring. In this study, we investigated (1) whether females of the European earwig Forficula auricularia avoid areas contaminated with spores of the entomopathogenic fungus Metarhizium brunneum prior to and at egg laying, as well as (2) whether spore presence entails an increase in females' investment into both pre-hatching forms of care and clutch quantity and quality. Our results first show that females did not avoid contaminated areas prior to and at egg laying. However, females returned to their eggs faster in presence of living spores compared to UV-killed or no spores. They were also more likely to construct a nest when in presence of both living and UVkilled spores (but only in one studied population). Finally, we found that spore presence did not influence maternal investment into egg grooming, egg gathering and egg defence, as well as into clutch quantity and quality. Overall, our results demonstrate that earwig females do not avoid contaminated environments, but could mitigate the associated costs of pathogen exposure by adjusting their level of egg care. These findings emphasize the importance of pathogens in the evolution of pre-hatching parental care and, more generally, in the emergence and maintenance of family life in nature.

Friend or foe? The apparent benefits of gregarine (Apicomplexa: Sporozoa) infection in the European earwig

“…These nutritional benefits could be particularly important in the European earwig, as females experience long periods of food deprivation over winter (Gingras and Tourneur, 2001;Kölliker, 2007;Tourneur and Meunier, 2020) during which they also provide extensive and energetically costly forms of care to their eggs (Koch and Meunier, 2014;Diehl and Meunier, 2018;Van Meyel et al, 2019). Assuming that gregarines help to resist against starvation, having a large stock of gregarines in the gut before egg production (as we observed in September) might, therefore, ensure female survival over the coming periods of starvation and high energy demand.…”

“…During the subsequent weeks (i.e. all over winter), these mothers typically stop their foraging activities (Berleur et al, 2001;Kölliker, 2007;Tourneur and Meunier, 2020) to provide extensive forms of care to their eggs and then to their resulting juveniles (Gingras and Tourneur, 2001;Kölliker, 2007;Meunier et al, 2012;Boos et al, 2014;Thesing et al, 2015;Diehl and Meunier, 2018).…”

Parental Microbiota Modulates Offspring Development, Body Mass and Fecundity in a Polyphagous Fruit Fly

“…This finding is in agreement with previous research in the pine weevil, showing that the hatching success of eggs laid by mothers with a native microbiota was significantly higher than that of axenic mothers [ 41 ]. While the mechanism is unclear, it is possible that the presence or absence of different microbes on the egg surface and in the egg environment (i.e., in the diet in our case) regulates egg hatching as shown in previous studies in insects and nematodes [ 42 , 43 , 44 ]. For instance, the close physical contact between common bacteria in the host’s intestine and the eggs of parasitic nematodes has been confirmed to regulate egg hatching, with incubations with different bacteria leading to different egg hatching percentages.…”

Variations in seasonal (not mean) temperatures drive rapid adaptations to novel environments at a continent scale

“…Females then burrow in the ground from mid‐fall to early winter and build a nest, where they lay their first clutch of eggs. After egg laying, females stop their foraging activity and provide extensive forms of egg care until hatching (Gingras and Tourneur , Boos et al , Koch and Meunier , Thesing et al , Diehl and Meunier , Körner et al ). The eggs of this first clutch hatch in spring and mothers remain with their newly hatched larvae for several weeks, during which mothers provide larvae with multiple forms of care (Gingras and Tourneur , Kölliker et al , Kramer et al ) and larvae exhibit forms of sibling cooperation (Falk et al , Kramer et al , Kramer and Meunier , Körner et al ).…”