Amphibian fungal disease and the cutaneous microbiome

The International Union for Conservation of Nature (IUCN) estimates that over 40% of all known amphibians are currently at risk of extinction due to the cumulative effects of climate change, pollution, habitat loss, and disease. Tropical ecosystems may experience the greatest decline, likely threatening to push many species to extinction that we have not yet discovered. Amphibians are not well sampled in many areas of Central Africa, which contributes to the difficulty in resolving historical biogeography and phylogenetic relationships. Species distribution information is also essential in developing conservation priorities, particularly in identifying threats to restricted range species or those that may be affected by habitat destruction and/or climate change. Among the most urgent threats to amphibians is the fungal disease chytridiomycosis, which is already assumed to have caused the extinction of many species. This research sought to conduct an exhaustive inventory of amphibian fauna across Bioko Island, Equatorial Guinea. Bioko is adjacent to the Guinean Forests, one of the most amphibian species-rich areas in Africa. Over the course of 5 years (2009-2014) these surveys resulted in both new records and new species for Bioko Island, identified species of concern, and refined our knowledge of amphibian species distributions on the island. During this work, amphibians were also sampled for the presence of Batrachochytrium dendrobatidis (Bd) to determine the nature of chytridiomycosis infection across a wide range of Central African amphibian species. Results showing positive Bd yet no mortality led us to investigate the cutaneous microbiome, which has been shown to harbor anti-fungal properties in some species. Metabolites and bacteria were sampled via specific swabbing techniques in an attempt to accurately characterize the cutaneous environment. Recently developed techniques for metabolite extraction and HPLC analysis allowed us to identify over 100 distinct compounds from specially prepared foam tipped metabolite swabs. DNA extractions and qPCR analysis performed on bacterial swabs allowed us to quantify the relative abundance of the most common bacteria species found on the amphibian skin. Together, these results show that amphibians tend to have metabolite and bacterial profiles that match other individuals of their species. This suggests the microbiome may be specifically regulated by amphibians, and calls for continued research into the potentially symbiotic role that cutaneous bacteria may play in disease resistance for amphibians.