More Than Meets the Eye: Unraveling the Interactions Between Skin Microbiota and Habitat in an Opportunistic Amphibian

With amphibians still holding the record as the most threatened class of terrestrial vertebrates, their skin microbiota has been shown to play a relevant role in their survival in a fast-changing world. Yet little is known about how abiotic factors associated with different aquatic habitats impact these skin microorganisms. Here we chose the yellow-bellied toad (Bombina variegata), a small anuran that colonizes a wide range of wetland habitats, to investigate how the diversity and composition of both its bacterial and fungal skin communities vary across different habitats and with water characteristics (temperature, pH, and dissolved oxygen) of these habitats. Skin microbiota was sampled from 14 sites in the Province of Trento (Italy), including natural pools, ephemeral ponds, irrigation tanks, and farm ponds. Interestingly, the diversity of the two microbial components was also highly correlated. Close associations between both the diversity and composition of water and skin communities were noted for each habitat and sampling site, suggesting that water bodies actively contribute to the skin microbiota assemblage. In addition, water pH, temperature, and dissolved oxygen affected both bacterial and fungal diversity of skin. We confirmed the presence of Batrachochytrium dendrobatidis in skin samples of animals collected from eight waterbodies, as well as more than 60 microbial taxa previously associated with resistance to this pathogen. We concluded that both skin bacterial and fungal communities appear to be influenced by each other as well as by environmental communities and conditions, and these relationships connecting the whole ecosystem should be considered in future research concerning amphibian conservation.