Gut microbiota of dung beetles shows taxonomic turnover but relative functional stability

The dung beetle gut microbiota is essential for host health and plays a key role in regulating the biochemical processes underpinning grassland ecosystem functioning. Understanding how its taxonomic and functional composition varies across species may help predict the ecological consequences of changes in dung beetle communities driven by shifts in pastoral practices. Elucidating the mechanisms of microbial acquisition and potential transmission is also crucial. To this end, a multispecies survey of gut-associated prokaryotic and fungal communities was conducted in nine dung beetle species from a valley in the Alps, representing four tribes and three nesting strategies. All individuals were collected from cow dung to minimise dietary variation. Using an amplicon sequence variant (ASV)-based metabarcoding approach targeting the 16S ribosomal RNA (rRNA) gene and the internal transcribed spacer 2 (ITS2) region, taxonomic composition and predicted functional profiles were characterised. Prokaryotic communities exhibited strong host-dependent structuring: both alpha- and beta-diversity analyses revealed significant differentiation among species and tribes, consistent with host phylogeny and suggestive of phylosymbiosis. In contrast, fungal communities were weakly structured by host taxonomy, with extensive overlap among most species and a limited tribal signal, indicating a greater role of environmental acquisition. Despite pronounced taxonomic turnover, predicted functional profiles were relatively consistent across hosts. Fermentation and nitrogen-related pathways dominated prokaryotic communities, whereas fungal communities were largely saprotrophic, with similar trophic distributions among species. This decoupling between taxonomic composition and functional potential suggests substantial functional redundancy in dung beetle gut microbiota, supporting resilient microbial contributions to dung degradation and nutrient cycling in rapidly changing mountain pastoral ecosystems in the Alps.