How hindgut microbiota may shape sympatric speciation in an invasive phytophagous scarab

Following the introduction of new host plants, rapid evolutionary changes in invasive phytophagous insects can sometimes result in sympatric speciation. The underlying processes and facilitation factors are still to be investigated in detail. The role of hindgut microbiota is one of these factors. In this paper, we examined the differences in the gut microbiota of two species of Costelytra scarabs (Coleoptera: Scarabaeidae, Melolonthinae), one non-invasive [Costelytra brunneum (Broun)] and one invasive (Costelytra giveni Coca-Abia & Romero-Samper), for which several ecotypes were analysed. In terms of bacterial assemblages, we found significant variation between the invasive and the non-invasive species. Three main groups of bacteria contributed to these differences, namely Oxalobacteracea, Rhizobiales, and Porphyromonadacea, with the last two potentially providing advantages in the exploitation of a new host plant. Among these bacteria, Porphyromonadacea were systematically present in high proportion in the gut of the invasive species C. giveni. The occurrence of these bacteria might have contributed to the initial capability of this insect to feed and benefit from newly introduced host plants. Furthermore, this study also revealed significant differences in the gut bacterial communities of four C. giveni ecotypes, supporting the hypothesis that part of the gut microbiota in this invasive phytophagous insect is likely to have been acquired horizontally from the newly exploited niche