The heat cured the infection within weeks, and about 70 percent of the infected frogs survived the 15-week experiment, said lead researcher Anthony Waddle. Waddle and a team of biologists published the results last week in Nature magazine in the hope that their simple invention will help solve a huge wildlife problem.
Waddle built shelters of black brick and greenhouse netting.
“It will be freezing cold outside, but the moment you walk in. [the shelter] … I would just sweat a lot because of the humidity and the heat,” Waddle, a postdoctoral researcher at Macquarie University in Macquarie Park, Australia, told The Washington Post.
Chytridiomycosis, which stems from Batrachochytrium dendrobatidis, an aquatic fungus, was believed to have first been found in Asia in the 1930s before it quickly spread around the world through trade and travel. A contagious fungus that has driven dozens of species of amphibians to the brink of extinction causes breathing problems that lead to cardiac arrest in many amphibians.
Scientists have tried to spare the amphibians by removing infected species from their habitats, chemically disinfecting their habitats and heating their water sources to combat the fungus. In 2021, Waddle created a vaccine for frogs Batrachochytrium dendrobatidis. But he wanted to come up with a solution that the frogs could use themselves, especially in the winter when cases of chytridiomycosis are at their highest.
In December 2020, Waddle placed several green and gold frogs, which are endangered in the Australian state of New South Wales, near a metal fence that was cold on one side and hot on the other. Frogs gravitated to the warm side.
Then the researchers divided 66 infected frogs between warm and cold areas in their laboratory. Frogs in the warm area, which was about 86 degrees, fended off the infection, while those in the cool area, which was about 66 degrees, remained infected.
These results led the researchers to believe that the frogs would choose to live in a warm environment — and would benefit from it if the researchers created one.
The researchers used their hardware supplies for the main experiment: clay bricks, black paint, greenhouse netting, and duct tape. They painted the bricks black to attract heat from the sun. Then they stacked 10 bricks on top of each other, each with 10 small holes. They covered several stacks of bricks with greenhouse netting to keep in the heat, and zip ties stabilized the shelters.
“I didn’t think it would work because of its simplicity,” Waddle said.
At Macquarie University’s campus in July 2021, researchers placed shelters in tubs of gravel, water, artificial plants and flower pots to mimic typical frog habitats. Then, 239 frogs were placed in tubs and given a choice between an unshaded shelter or a fabric-shaded shelter. Most were drawn to the warmth of bricks in unshaded shelters.
Unshaded shelters were about eight degrees warmer than shaded habitats, and it made a difference. About a month after the experiment began, the researchers swabbed the frogs’ skin and found that the infection healed most quickly in frogs in unshaded shelters.
In November 2021 – shortly before the start of the austral summer – 167 of the 239 frogs were still alive, Waddle said. Wild frogs usually begin to die about three weeks after they are infected, according to the Ohio Department of Natural Resources.
The researchers also found that frogs that survived chytridiomycosis became more resistant to the disease — a promising sign for the survival of a species that can live about 15 years in captivity.
Bryan Pijanowski, a professor of forestry and natural resources at Purdue University, said in an email to The Post that the shelters Waddle built offer “some optimism” for addressing a disease that has wiped out at least 90 species of amphibians.
“These are dire numbers that require new approaches to turn the tide,” he said.
Waddle has set up several shelters in Sydney Olympic Park, Australia, home to one of the largest remaining populations of green and gold frogs. He plans to monitor the population for the next few years.
He said that he he hopes parks and homeowners will implement their own “frog saunas.” He created a public guide to building them, estimating they cost about $80 each.
“Conservation research is a big loss,” Waddle said. “You just try things and they don’t work. You try things and they don’t work. But we got something, and it’s something we can deliver now.”