The chytrid fungus Batrachochytrium dendrobatidis, or Bd, causes a deadly disease called chytridiomycosis that has wreaked havoc on amphibian populations across the globe. An astounding 90 species have been lost due to chytridiomycosis infections and 500 other species are in decline, with further extinctions likely. Amphibian chytridiomycosis is thought to be responsible for the most significant known loss of biodiversity due to a single disease.
Once common in southeastern Australia, green and golden bell frogs are just one of the species vulnerable to chytridiomycosis. But at least for these endangered frogs, there is a glimmer of hope. Led by Dr. Anthony Waddle, scientists at Macquarie University in Sydney and the University of Melbourne created “frog saunas” in greenhouses to provide warm conditions in which the frogs could raise their body temperatures and fight off the fungus. Despite the fancy name, the saunas are essentially just black, sun-heated masonry bricks with holes where the frogs can take refuge.
These hot, steamy spots are especially critical during the winter (June, July, and August in the Southern Hemisphere), when amphibians often struggle to warm themselves up. When the frogs can raise their temperatures, the fungus, which thrives in cool environments, poses less of a threat, and the frogs are more likely “to cure their infections, or not even get sick at all,“ according to Waddle. The researchers also found that frogs that had recovered with the assistance of the brick saunas were around 23 times more likely to become resistant to future chytridiomycosis infections.
Interestingly, other experiments that have sought to raise the frogs’ temperature to fight off chytridiomycosis, such as increasing sun exposure, installing heated ponds, and raising the ground and water temperature, have failed to produce results. The brick saunas for green and golden bell frogs appear to be the first successful outcome. However, scientists aren't sure whether the frog sauna technique would work on other species. While they might be used by frogs in warm climates, those that live in cool environments would be too stressed by the heated bricks. Other solutions will undoubtedly be needed to eradicate the amphibian chytrid fungus, which is now widespread everywhere from rainforests to glacial ponds. Waddle compared its prevalence to the common cold in humans.
Enjoying the steam and fighting for their lives:
- First identified by scientists in 1998, Bd is responsible for the extinction of species ranging from the Kihansi spray toad in Tanzania to the claw-toothed salamander in Mexico. The fungus attacks proteins in the skin of the afflicted amphibian and ultimately results in heart failure.
- Previously, the only way to treat chytridiomycosis infections was to bring the frogs into captivity and use fungicidal drugs. More recently, vaccines and chemical treatments have also been developed.
- Not all frog species are harmed by Bd, which spreads via water and contact among amphibians. For example, American bullfrogs can infect other species with the fungus without becoming sick themselves.
- Waddle hopes that more amphibian species will eventually evolve mutations to resist the disease, but this will take a significant amount of time.