The microbes residing within the gut of an animal host often maximise their own fitness by modifying their host's physiological, reproductive, and behavioural functions. Whereas recent studies suggest that they may also shape host sociality and therefore have critical effects on animal social evolution, the impact of the gut microbiota on maternal care remains unexplored. This is surprising, as this social behaviour is widespread among animals, often determines the fitness of both juveniles and parents, and is essential in the evolution of complex animal societies. Here, we address this gap in knowledge by testing whether life-long alterations of the gut microbiota with rifampicin - a broad-spectrum antibiotic - impair the expression of pre- and post-hatching maternal care in the European earwig, an insect exhibiting extensive forms of maternal care towards eggs and juveniles. Our results first confirm that rifampicin altered the mothers' gut microbial communities and revealed that the composition of the gut microbiota differs before and after egg care. Contrary to our predictions, however, the rifampicin-induced alterations of the gut microbiota did not modify the expression of pre- or post-hatching care. Independent of maternal care, rifampicin increased the females' feces production and resulted in lighter eggs and juveniles. By contrast, rifampicin altered none of the other 23 physiological, reproductive and longevity traits measured over the females' lifetime. Overall, these findings reveal that altering the gut microbiota does not necessarily affect host sociality. More generally, our results emphasize that not all animals have evolved a co-dependence with their microbiota.
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