Climate Drives Amphibian Skin Microbiology at the Global Scale

Yes, there exists a well-trained community of scientists that dedicate their lives to the ecology and function of frog skin. Although, we come from different backgrounds, our central goal of amphibian conservation is uniquely unifying, in a way that allows for open collaboration.

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The team of contributors to this paper, all love “Frogging’. For us, this is heading out to locate amphibian species desired for swabbing, photographing or just to enjoy their behaviors. We find ourselves, at the tops of wind-swept mountains, glacial lakes, or way off the trail in tropical streams in the middle of the night. There’s a connection between you and the environment when you are really putting yourself out there.

Our research paper (HERE) extends what has been learned from individual studies in a way that pushes ecology of a threatened class of vertebrates from the microbial scale to the ‘macrobial’ scale. The take home lesson of our synthesis is that microbes of amphibian skin are principally determined by climatic conditions. This result places all individual amphibian studies in a larger context and allows us to make comparisons across species and space in a more precise way. We also gain a new perspective on global microbial diversity patterns.

As we push this research project out of the ‘nest’, into the scientific community and the greater public, it is easy to become reminiscent about how this all began. Sitting at a small wooden table, our core group decided ‘now’ would be the perfect time to merge all the studies, data, and effort that has gone into exploring and explaining the skin bacterial communities of the frogs and salamanders we all hold near to our hearts. The result of all these individual lab’s efforts, largely collected in the context of defense against amphibian skin pathogen Batracochytridium dendrobatedis (Bd), was an enormous amount of skin microbial data that was prime to synthesize and to robustly test the drivers of amphibian skin diversity and composition. Our goal was to “scale up” and explore microbial biological diversity at the global scale. Jordan Kueneman and Molly Bletz, joint lead authors, lived and breathed “amphibian skin microbes” as they completed their Phd’s on frog skins, spending who-knows-how-many- hours in the lab extracting DNA, and reanalyzing the data zillions of times in order to convince themselves and the reviewers that the global signal in these data is real.

Armed with samples and data from many locations and countries, there was only one important piece missing; a way to independently evaluate climate effects from host species effects. To do this, we set out to capture and sample American Bullfrogs from as many places as possible. American Bullfrogs have been uniquely introduced around the world as a consequence of frog farming for human consumption. Traveling the world to sample one particular specie of frogs may seem to most like a bazar task, but for us, it was essential. This essential element of the study helps independently confirm the global patterns of bacterial diversity that we observe in our study. We anticipate this is only the beginning, and that future large scale datasets will continue to offer new insight into the global distribution of microbial organisms.

Indeed, microbial communities provide many extended functions for their hosts, allowing them to expand their range of nutritional resources, training the immune system, stimulating developmental processes and, importantly for amphibians, protecting them from pathogens. The overwhelming evidence suggests that amphibian skin microbiomes are critical for amphibian health, microbial associations are targets of host selection, and promoting beneficial microbial communities of amphibians is an obtainable frontier for amphibian conservation.

Global amphibian decline, driven by globally invasive skin pathogen Bd, is a crisis that brings many researchers together to seek solutions. Amphibians, often viewed as environmental indicators, are singing in a cacophony to get our attention. The unpleasant reality is that globalization also means globalization of pathogens. Thus, many locally evolved pathogens can be moved to novel environments where, much like small pox, there is no native immunity and the results of this are devastating. In this modern age of connectedness, the consequences of Bd on the global scale are enormous. The amphibian disease crisis has become a rallying cry for conservation biologists. As a result, amphibian disease ecology research is blazing a trail for understanding how generalist pathogens move in the environment and the how diverse hosts respond to these introductions. The active response to this crisis has made a splash, creating new approaches in disease management and wildlife conservation. Novel approaches to disease management are paramount to mitigating the effects of fungal disease of bats, and corals, as well as additional emerging diseases of amphibians. Understanding the influence of climate on animal-microbiomes offers an important lens, particularly when working to design microbial therapeutics for threatened or endangered wildlife.

Jordan Kueneman

Research Scientist, Smithsonian