As part of ongoing global biodiversity losses, dramatic declines in amphibian diversity have been documented throughout the Neotropics. Among the threats to amphibian diversity is the skin disease chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd). Several recent studies suggest that amphibian skin microbial communities can alter the outcome of the amphibian-Bd interaction, and that Bd might be posing a selective pressure upon these microbial communities in wild populations. However, an understanding of how environmental conditions impact the function of these microbial communities is scarce. Variable functions of these symbiotic microbes under different contexts might explain why experiments testing potential amphibian probiotics have obtained mixed results. Given the variation in chytridiomycosis outbreaks across elevations, we aimed to determine how the diversity, structure and function of these symbiotic microbial communities changes with elevation. We collected skin swab samples (N=60) in Panamá from three high and three low elevation populations of Silverstoneia flotator, a species thought to be tolerant to Bd. These populations represent a range of environmental conditions, with more dramatic Bd outbreaks at high elevation sites. To assess the skin bacterial communities and metabolite profiles, we used 16S rRNA gene amplicon sequencing and HPLC-MS, respectively.
Our results indicate that across high and low elevations, individuals harbor similar skin bacterial communities, although one lowland site appeared to differ from the others. Interestingly, we found a geographical pattern, with bacterial richness (estimated as the number of Operational Taxonomic Units, which approximates bacterial species) decreasing from west to east. This coincides with the direction of the advancement of Bd through Panama. Moreover, the metabolite profiles suggest that there is significant variation among frog populations (i.e. sites) and between elevations. Overall, these results suggest that while the frogs have similar bacterial community structure, the local environment might be shaping the metabolites profiles, which indicate a potential functional plasticity that could influence the interaction with Bd. Climate change and unprecedented habitat lost present a new frontier in ecological research; it is critical to consider the context-dependence of amphibian-microbes-Bd interactions to inform amphibian conservation efforts in the Neotropics.