Earwig mothers can boost offspring’s defence against pathogens during postoviposition care

Abstract

An important function of parental care is to ensure the survival of offspring against pathogens. In insects, it was long believed that this function was limited in scope and time and consisted mainly of parental behaviours reducing contact between offspring and pathogens. However, recent data show that insect parents can also improve offspring’s defence against pathogens by transferring their acquired immune experience to the eggs during oogenesis. Here, we investigated whether this parental protection could be extended to include postoviposition care. We addressed this question in the European earwig, Forficula auricularia, an insect in which mothers provide extensive forms of care to their eggs and juveniles. We immune-challenged mothers with dead bacterium Serratia marcescens or control solutions while they were caring for their eggs and then monitored the survival rate of these mothers and their resulting adult offspring after a new infection by the same live pathogen. In line with our prediction, we found that both the mothers that were immune-challenged after oviposition and the adult offspring reared by these immune-challenged mothers had the highest survival after infection. However, what triggered this higher survival rate was the wounding of the mothers and not their previous exposure to dead bacteria. Our data also show that these higher survival rates were not associated with changes in the expression of maternal egg care or offspring quality. Overall, our findings shed light on a novel benefit of postoviposition parental care in insects. More generally, they support the recent claim that access to social immunity by offspring may play a key role in the early emergence and maintenance of family life in animals.