The heat cured the infection within a few 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, hoping that their simple invention will help solve a major problem in nature.
Waddle built the shelters using black bricks and greenhouse netting.
“It may be freezing outside, but once you step inside, [the shelter] “…I would just sweat profusely because of the humidity and the heat,” Waddle, a postdoctoral researcher at Macquarie University in Macquarie Park, Australia, told The Washington Post.
Chytridiomycosis, which results from Batrachochytrium dendrobatidisa waterborne fungus, was first found in Asia in the 1930s, before trade and travel caused it to spread rapidly around the world. The infectious fungus, which has driven dozens of amphibian species to the brink of extinction, causes respiratory problems to the point that the hearts of many amphibians stop working.
Scientists have tried to save amphibians by removing infected species from their habitats, chemically disinfecting their homes, and heating their water sources to combat the fungus. In 2021, Waddle created a vaccine for frogs against Batrachochytrium dendrobatidisHowever, he wanted to come up with a solution that frogs could use themselves, especially in winter, when most cases of chytridiomycosis occur.
In December 2020, Waddle placed a pair of green and gold bell frogs, which are endangered in the Australian state of New South Wales, near a metal fence post that was cold on one side and warm on the other. The frogs migrated to the warm side.
Next, researchers divided 66 infected frogs into warm and cold areas in their lab. The frogs in the warm area, which was about 86 degrees, fought off the infection, while the frogs in the cold area, which was about 66 degrees, remained infected.
These results led researchers to believe that frogs would choose to live in a warm habitat and would benefit if researchers created one.
Scientists used their hardware supplies for the main experiment: clay bricks, black paint, greenhouse nets, and zip ties. They painted the bricks black to attract heat from the sun. Then they stacked 10 bricks, each with 10 small holes, on top of each other. They covered multiple stacks of bricks with greenhouse netting to trap heat, and the 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 the shelters in containers filled with gravel, water, artificial plants and flower pots to mimic the frogs’ typical habitats. They then placed 239 frogs in the containers and gave them a choice of a shelter with no shade or a shelter with a cloth in the shade. Most were attracted to the warmth of the rocks in the shelters with no shade.
The unshaded shelters were about eight degrees warmer than the shaded habitats, and that made a difference. About a month into the experiment, researchers swabbed the frogs’ skin and found that the infection cleared up fastest in frogs in the unshaded shelters.
As of November 2021 — shortly before the austral summer began — 167 of the 239 frogs were still alive, Waddle said. Wild frogs typically begin dying 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 the species, which can live for 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 a “little bit of optimism” for solving a disease that has wiped out at least 90 amphibian species.
“These are staggering numbers that call for new approaches to turn the tide,” he said.
Waddle has set up a few shelters in Sydney Olympic Park, Australia, which is home to one of the largest remaining populations of green and golden bell frogs. He plans to monitor the population over the next few years.
He said that he hopes that parks and homeowners will implement their own “frog saunas.” He created a public guide for building them, estimating that they cost about $80 each.
“Conservation research is a lot of waste,” Waddle said. “You just try things, they don’t work. You try things, they don’t work. But we have something, and it’s something we can deliver right away.”