Gut content metabarcoding and citizen science reveal the earthworm prey of the exotic terrestrial flatworm, Obama nungara

The metabarcoding of digestive contents is a powerful approach to study the diet of newly introduced predatory species, and therefore to forecast their potential impact on native species. Obama nungara (Platyhelminthes: Geoplanidae) is an exotic terrestrial flatworm, which recently invaded several Western European countries and predates on earthworms. Because O. nungara is known to live above ground, we hypothesize that it consumes earthworms living on or coming frequently to the soil surface i.e. epigeic or anecic species, respectively. In this study, we undertook the metabarcoding of O. nungara gut contents to characterize more precisely the earthworm prey it consumes in its invaded range. This species is only known to date in anthropized, mostly privately-owned, environments and the contribution of citizen science volunteers to the reporting of species and their collection is of critical value. We first validated the development of the method, by extracting the digestive contents of O. nungara obtained through citizen science contributions throughout France, amplifying a 70bp earthworm-specific fragment of the 16S RNA gene and sequencing amplicons with a high-throughput approach. Secondly, the taxonomic affiliation of the sequences allowed identifying one to five species of earthworms in the digestive content of each flatworm. Contrary to our hypothesis, O. nungara seems also to consume endogeic species living within the soil and rarely coming out to the surface, as well as intermediate ecological categories. These results, by expanding the range of potential prey of O. nungara, confirm its status as a threat to native soil fauna.