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Frog ‘saunas’ may help threatened frogs fight off deadly fungus

  • Researchers have developed simple, sun-heated shelters that allow frogs to raise their body temperatures and fight off a deadly fungal disease called chytridiomycosis.
  • The study focused on the green and golden bell frog in Australia, a threatened species, showing that frogs given access to these warm shelters cleared infections faster and developed resistance to future infections.
  • This innovative approach could provide a valuable, low-cost tool for protecting various amphibian species threatened by the fungal disease, which has devastated amphibian populations worldwide.
  • The research comes at a critical time, as a recent study found that two in five amphibian species are now threatened with extinction, with climate change becoming a primary threat.

Researchers have developed simple, sun-heated shelters that allow frogs to raise their body temperatures and fight off infections. These frog “saunas” may bring hope for populations threatened by a deadly fungal disease, according to a new study published in Nature.

Researchers found that providing artificial “hotspot” shelters allows frogs to quickly bake off infections by raising their body temperatures. The shelters were constructed using simple materials like bricks and small greenhouses.

“In these simple little hotspots, frogs can go and heat up their bodies to a temperature that destroys the infections,” lead author Anthony Waddle, a researcher at Macquarie University in Australia, said in a release.

The research team focused on the green and golden bell frog (Litoria aurea), a species listed as vulnerable to extinction, which has disappeared from more than 90% of its native range in Australia since the fungal disease chytridiomycosis arrived in 1978.

Adult green and golden bell frog (Litoria aurea) on brick in the sauna chambers. Photo courtesy of Anthony Waddle.

“[The species] used to be very common across eastern Australia; they lived in letterboxes and backyards and really adapted to human settlements, before chytridiomycosis came and hammered the population,” Waddle said.

Since it was first identified, Chytridiomycosis has driven at least 90 amphibian species to extinction. Another 124 species have seen population declines of more than 90%.

“In the 25 years since chytridiomycosis was identified as a major cause of the global collapse of amphibian populations, our results are the first to provide a simple, inexpensive and widely applicable strategy to buffer frogs against this disease,” Waddle said.

The fungus that causes chytridiomycosis thrives in cool conditions, and can’t tolerate temperatures higher than 30° Celsius (86° Fahrenheit). The researchers discovered that green and golden bell frogs naturally prefer temperatures around 29°C (84°F), which, over a sustained period, is much higher than the fungus can tolerate.

In laboratory experiments, frogs given access to warmer temperatures were able to clear their infections more quickly than those kept in cooler conditions. Importantly, frogs that recovered from an infection this way also developed resistance to subsequent infections.

To test the effectiveness of the hotspot shelters in a more realistic setting, the team conducted a 15-week experiment using outdoor enclosures designed to mimic the frogs’ natural habitat. They found that frogs infected with chytridiomycosis cleared the infection faster when they had access to unshaded, warmer shelters compared to shaded ones.

Frog saunas set up in the wild. Photo courtesy of Anthony Waddle.

The study showed that frogs who survive an infection can develop a form of acquired immunity, making them more resistant to future infections. When reexposed to the fungus, these “pathogen-experienced” frogs had a much higher survival rate (86%) compared to frogs that hadn’t been previously infected (22%).

“Chytrid isn’t going away, but our behavioural ecology intervention can help endangered amphibians co-exist with chytridiomycosis in their ecosystems,” Richard Shine, a senior author on the study and professor at Macquarie University, said in the release.

The research team is now working on expanding the study and implementing the hotspot shelters in one of the largest and most vulnerable populations of green and golden bell frogs, at Sydney Olympic Park. The shelters are made from cheap and readily available materials, making them easy to implement.

“We’ve shown that it works; now we’re putting it into one of the most vulnerable populations where we expect to see immediate impact,” Waddle said.

Dr. Anthony Waddle holds a green and golden bell frog (Litoria aurea). His team developed frog saunas to help frogs fight off chytrid fungus. Photo by Yorick Lambreghts

This development comes at a critical time for amphibians globally. A separate study published in 2023 found that more than 8,000 amphibian species are at a substantially higher risk of extinction than they were in 2004. Two in five amphibians are now threatened with extinction, making them among the most imperiled animal groups.

Jennifer Luedtke Swandby of the conservation NGO Re:wild, who was not involved in the hotspot shelter study, said climate change has become the primary threat for 39% of amphibian species that moved closer to extinction between 2004 and 2022.

“Amphibians are becoming climate captives,” Swandby said, “unable to move very far to escape the climate change-induced increase in frequency and intensity of extreme heat, wildfires, drought and hurricanes.”

While the researchers caution that the hotspot shelter strategy may not work for all amphibian species, particularly those adapted to cooler climates, it could provide a valuable tool for protecting threatened amphibians.

“By protecting amphibians, we are protecting the forests and ecosystems that are key … solutions to battling climate change,” Kelsey Neam, a co-author of the 2023 amphibian extinction risk study, told AFP. “An investment in amphibians is an investment in the future of our planet.”

Green and golden bell frogs inside a brick “baking off” fungal infection. Photo by Anthony Waddle.

Banner image of the green and golden bell frog (Litoria aurea) in the hot spot saunas. Photo courtesy of Anthony Waddle.

Liz Kimbrough is a staff writer for Mongabay and holds a Ph.D. in ecology and evolutionary biology from Tulane University, where she studied the microbiomes of trees. View more of her reporting here.


Waddle, A. W., Clulow, S., Aquilina, A., Sauer, E. L., Kaiser, S. W., Miller, C., … Shine, R. (2024). Hotspot shelters stimulate frog resistance to chytridiomycosis. Nature, 1-6. doi:10.1038/s41586-024-07582-y

Luedtke, J. A., Chanson, J., Neam, K., Hobin, L., Maciel, A. O., Catenazzi, A., … Stuart, S. N. (2023). Ongoing declines for the world’s amphibians in the face of emerging threats. Nature. doi:10.1038/s41586-023-06578-4


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