Artificial Warming Chambers Combat Chytrid Fungus in Frogs

Infectious diseases have disproportionately affected amphibians as global diversity continues to decline due to various factors. An unhealthy fungus known as chytridiomycosis, or simply "chytrid," has caused the extinction of 90 amphibian species and the decline of 500 more.

New findings about "frog saunas" give hope. Imagine a big, sun-heated brick building with cubby holes where frogs can seek shelter from colder weather instead of the classic wood sauna.

The researchers hypothesized that if green and golden bell frogs were offered the chance to warm up in artificial saunas, they would seize the chance because chytrid attacks frogs more severely in the winter. It turns out that they could eradicate the infection by increasing their body temperature in addition to seizing the chance.

The frogs were not given any incentives to enter the saunas in both natural and lab environments. The frogs warmed up to the saunas like Finns in the winter. The researchers discovered that frogs who had been infected initially and had recovered from it after using the sauna had a much lower chance of contracting the infection again.

The study was published in the journal Nature. Twelve of the 14 co-authors are from Australia, the country where the study was carried out. Erin Sauer, a Postdoctoral Fellow in Biological Sciences at the University of Arkansas, is the only co-author from North America.

Sauer's earlier studies on the relationship between amphibian thermoregulatory behavior and chytrid resistance impeded the team's work on frog saunas. To measure the frogs' preferred temperatures, Sauer created thermal gradients that she could hold in for extended periods for that 2018 study.

To apply practically, this meant covering sections of the aluminium gutter with a Plexiglas lid with cooling and heating elements on opposite ends to create a temperature gradient between them. In the end, she discovered that species that favored higher temperatures could recover from their infections by congregating near the warmer regions of thermal gradients.

Anthony Waddle, the lead author on the Nature paper, got in touch with me because he wanted to build my thermal gradients in Australia and replicate my study with green and golden bell frogs. So, I helped him design his set up and experiment in 2020-2021, and then helped with the data analysis for the lab study.”

Erin L. Sauer, Postdoctoral Fellow and Study Co-Author, Biological Sciences, University of Arkansas

Sauer continued, “Very similar to my 2018 study, we found that the green and golden bell frogs preferred warm temperatures and were able to better resist their chytrid infections at those warm temperatures. Anthony and his colleagues in Australia then applied the findings from the lab experiment to build the frog saunas and run the mesocosm experiment.”

Although the results indicate that the public can prevent the extinction of green and golden bell frogs by erecting inexpensive saunas in gardens or wetlands, Sauer issues a warning that this will not benefit all frog species. 

My research has shown that while warm adapted species have better disease outcomes at warm temperatures, cold adapted species actually have worse outcomes at warm temperatures. My colleagues and I have termed this phenomenon the ‘thermal mismatch hypothesis’ and did a global study testing our hypothesis across systems a few years ago that was published in Science. So, unfortunately, the frog saunas won't work for all species but work beautifully for the warm-preferring green and golden bell frogs.” 

Erin L. Sauer, Postdoctoral Fellow and Study Co-Author, Biological Sciences, University of Arkansas