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 contribute to solving a massive wildlife issue.
Waddle built the shelters using black bricks and greenhouse netting.
“It will be very cold outside, but the moment you step inside [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 is derived from Batrachochytrium dendrobatidis, a waterborne fungus, was believed to have first been found in Asia in the 1930s before trade and travel caused it to spread rapidly around the world. The contagious fungus, which has driven dozens of amphibian species to the brink of extinction, causes breathing problems until the heart of many amphibians stops.
Scientists have tried to save the amphibians by removing infected species from their habitats, chemically disinfecting their homes and heating their water sources to fight the fungus. In 2021, Waddle created a frog vaccine against Batrachochytrium dendrobatidis. However, he wanted to devise a solution that the frogs could use themselves, especially in the winter when cases of chytridiomycosis are highest.
In December 2020, Waddle placed several green and golden bell frogs, which are endangered in the Australian state of New South Wales, next to a metal fence that was cold on one side and hot on the other. Frogs gravitated toward the warm side.
The researchers then divided 66 infected frogs between warm and cold areas in their lab. Frogs in the warm zone, which was about 86 degrees, fought off the infection, while those in the cold zone, which was about 66 degrees, remained infected.
These results led the researchers to believe that the frogs would choose—and benefit from—living in a warm habitat if the researchers were to create one.
The scientists used their own equipment for the main experiment: clay bricks, black paint, greenhouse netting and cable ties. They painted the bricks black to attract heat from the sun. They then stacked 10 bricks, each containing 10 small holes, one on top of the other. They covered multiple brick stacks with a greenhouse grid to retain heat, and cable ties stabilized the shelters.
“I didn’t think it would work because of its simplicity,” Waddle said.
At the Macquarie University campus in July 2021, researchers set up the enclosures in tubs of gravel, water, artificial plants and flower pots to mimic typical frog habitats. The 239 frogs were then placed in tubs and given a choice between a shelter without shade or a shelter covered with a cloth. Most are drawn to the warmth of bricks in shadeless shelters.
Unshaded habitats were about eight degrees warmer than shaded habitats, and that made a difference. About a month into the experiment, the researchers swabbed the frogs’ skin and found that the infection was healing faster in the frogs in the unshaded shelters.
By November 2021 – just before the start of Australia’s summer – 167 of the 239 frogs were still alive, Waddle said. Wild frogs usually begin to die about three weeks after being 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 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 built by Waddle offer “some optimism” for solving a disease that has wiped out at least 90 amphibian species.
“These are dire numbers that require new approaches to change course,” he said.
Waddle has set up several shelters in Sydney’s Olympic Park, Australia, home to one of the largest remaining populations of green and golden bell frogs. He plans to monitor the population for the next few years.
He said that he hopes that parks and homeowners will implement their own “frog saunas.” He created a public guide to building them, estimating that each one costs about $80.
“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 offer immediately.”