Habitat disturbance interacts with Bd infection to shape the skin bacterial communities of an Amazonian frog

Lia Schlippe Justicia, Susana Ferreira, Franz Hoelzl, Carolin Dittrich, Martin Mayer, Bibiana Rojas

Amphibians are the most threatened vertebrate class globally, with habitat alteration and the fungal pathogen Batrachochytrium dendrobatidis (Bd) representing two major and often co-occurring drivers of decline. However, how these stressors interact to shape host-microbiome-pathogen dynamics remains poorly understood. Here, we investigated whether variation in anthropogenic habitat disturbance, quantified using the Human Footprint Index (HFI), influences Bd infection patterns (prevalence and intensity) and skin bacterial community structure in six populations of the Neotropical poison frog Dendrobates tinctorius. We characterized alpha and beta diversity of both the overall skin bacterial community and the subset of putative Bd-inhibitory taxa. Bd infection probability increased with increasing HFI and with frog spatial proximity. While HFI alone had limited direct effects on skin microbiome composition, its interaction with Bd load was associated with reduced bacterial alpha diversity and increased community dispersion. Similarly, within the Bd-inhibitory bacterial subset, relative abundance was higher in frogs with both high Bd loads and in disturbed sites. Together, our findings suggest that anthropogenic disturbance may not directly restructure amphibian skin microbiomes, but instead intensifies pathogen-associated microbial changes, highlighting the importance of considering interacting global change stressors in amphibian disease ecology.