Wedged into the tiny holes of masonry bricks, which heat their bodies up to near 30 C, you might think Australian green and golden bell frogs would be uncomfortable.
But new research says the amphibians love it, and that these DIY dry saunas — made with spray-painted bricks housed in plastic greenhouses — could give them an edge in fighting a deadly fungus.
“This is really exciting,” said Anthony Waddle, a biologist at Macquarie University in Sydney, Australia, and lead author of the new study published in Nature. “If frogs are given the opportunity, they can [help] themselves.”
Waddle and his team designed experiments involving easily obtained materials, setting these makeshift saunas up in a semi-wild habitat on Macquarie University campus to see if frogs would use them to fight off a global killer.
The fungus is Batrachochytrium dendrobatidis (shortened to Bd, but also referred to as chytrid, pronounced kit-rid), and it is responsible for declines in the population of more than 500 amphibian species — and the extinction of at least 90 others.
“I think it’s been one of the most devastating pathogens that Western science has recorded,” said Christina Davy, a biologist at Carleton University in Ottawa, who was not involved with the study.
“It infects the skin of the amphibians and it interferes with their ability to move water and gases across their skin,” explained Davy.
Waddle compared chytrid’s effects to an athlete who drinks too much water, disrupting the body’s sodium and potassium levels, eventually leading to cardiac arrest.
Davy adds that chytrid is fast-acting, hardy, can spread without hosts and is found around the world. When it enters a new area, previously uninfected and endangered species can be wiped out.
A brick house
But before you imagine an amphibian version of the spores in The Last of Us, chytrid does have preferences — and really hot temperatures, close to 30 C, are not among them.
Waddle and his team worked with green and golden bell frogs, an endangered species that’s native to New South Wales. After infecting frogs with chytrid, they created mesocosms — a controlled outdoor environment — of different frog habitats. These included the so-called frog saunas, and the resulting toasty and humid climate was highly preferred by the frogs, Waddle explained.
But he also found that when “frogs had access to these shelters, their body temperatures were higher and over time they had lower infections.” On top of that, frogs that cleared their infections using this high heat were more resistant to re-infection.
Ana Longo, an amphibian disease expert and biologist at the University of Florida, called the experiment simple yet elegant, but cautioned that it faces challenges in how it would scale to other species and in the wild.
“Amphibians are so diverse and they have so many different habitat preferences,” she said from Gainesville, Fla.
However, Longo says when it comes to a threat as devastating as chytrid, there are few tools available outside of a controlled zoo environment, such as anti-fungal treatments.
“We need bold measures at this point,” Longo said. “We know that [a] single measure is not going to be effective across all the species. So I think we just have to try different things.”
Waddle says the materials cost him around 70 Australian dollars. Both Davy and Longo appreciated how approachable and affordable this solution could be for anyone to build.
Why save the frogs?
Amphibians are part of numerous food webs, and Waddle says they bring benefits to aquatic environments in their early lives as larvae and tadpoles, as well as to the land once they mature.
Both predator and prey, they are critical to healthy snake populations as well as keeping insect populations down. In fact, when chytrid killed off frog populations in Costa Rica and Panama, there was a spike in cases of malaria.
While his team’s solution isn’t permanent, it would give the frogs a fighting chance during colder seasons where chytrid thrives.
“Right now, they just get hammered every winter. There’s just dead and dying frogs everywhere,” Waddle said, describing what he has seen in Sydney. “Populations are just struggling to get a couple individuals through the winter to breed.”
While declines in frog species from chytrid have been observed around the world for decades, Davy at Carleton University says it doesn’t always kill. Her own research found it to be widespread in Ontario in frogs and salamanders, and doesn’t result in mass death.
But she warns that tolerance may not apply to newer strains.
“There’s real concern right now about bringing a new species of chytrid fungus to North America,” Davy said. “And there’s real concern that if it reached [the continent] … it could also be really devastating.”
