DNA metabarcoding of the gut microbiota in an Italian alpine dung beetle community

Dung beetles (Coleoptera: Scarabaeoidea) play a key role in several ecological processes and services, including dung removal, maintaining soil fertility, nutrient cycling, and reducing greenhouse gas emissions. The gut microbiota of dung beetles is involved in many of these ecological services. In the present study, we analysed the gut microbiota of 12 species belonging to five different tribes and different functional groups based on their nesting strategies. Ten wild individuals per species were collected from cattle dung in the Western Alps. We analysed the prokaryotic and fungal communities using high-throughput sequencing of the 16S rRNA gene and the ITS2 region, respectively. To assess microbiota variation, we applied distance-based redundancy analysis (db-RDA) using Bray-Curtis dissimilarity and conducted envfit analyses to determine which factors best explained microbial community composition. For prokaryotes, host species identity accounted for the greatest variation (R² = 86.6%, p = 0.001), followed by tribe (R² = 60.6%, p = 0.001) and functional group (R² = 52.6%, p = 0.001). A similar trend was observed for fungal communities, with host species again explaining the most variance (R² = 78.1%, p = 0.001), though tribe (R² = 28.3%, p = 0.001) and functional group (R² = 27.6%, p = 0.001) had lower explanatory power. Interestingly, db-RDA results showed that dung beetle species differed more in their prokaryote than fungal composition. Furthermore, species accumulation curves indicated that microbial diversity increases with the number of dung beetle species included, highlighting the importance of taxonomic breadth in microbial studies. These results suggest that when dung beetles have a uniform diet, host phylogeny is the dominant factor shaping the gut microbiota, with significant implications for understanding gut microbial diversity of dung beetle communities.