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If you give a frog a sauna, it might fight off a deadly fungus

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For decades, a deadly fungal disease has plagued amphibians around the world, wiping out frogs, toads and salamanders from mountain lakes in the United States to rainforests in Australia. The disease is called chytridiomycosis, or chytrid, and it causes At least 90 It is estimated that this phenomenon has led to the extinction of hundreds of amphibian species and caused the decline of hundreds of other animal species.

“Chytridiomycosis is an unprecedented epidemic in wildlife,” said Anthony Waddle, a conservation biologist at Macquarie University in Sydney, Australia. “We are seeing the extinction of species and populations.”

But like many powerful enemies, the chytrid has an Achilles’ heel. The culprit is a fungus called Batrachochytrium dendrobatidis, or Bd for short, which thrives in cold weather and cannot withstand high temperatures.

Now, A new study Evidence suggests conservationists could stop fungal infestations by providing frogs with a warm place to overwinter. Researchers have found that a simple pile of bricks in the sun attracts Australia’s vulnerable green and golden bell frog. These thermal shelters raise the frogs’ body temperatures, helping them fight off fungal infections and perhaps preparing them for long-term survival.

“If we give frogs the ability to clear an infection through heat, they will do it,” said Dr. Waddell, lead author of the new paper, published Wednesday in the journal Nature. “And they may develop resistance in the future.”

The green and golden bell frog, once common in southeastern Australia, has disappeared from much of the landscape and is now Listed as endangered species Located in New South Wales.

In Sydney, where some of the last remaining bell frogs live, chytrid outbreaks often occur in winter and early spring, when daytime temperatures can reach as high as 60 degrees Fahrenheit. In the first of several experiments documented in the new paper, Dr. Wardle and his colleagues found that bell frogs prefer warmer climates when conditions allow. When placed in a habitat with a temperature gradient, bell frogs gravitated toward areas with an average temperature of 84 degrees Fahrenheit, which is warmer than the frog’s ideal.

In a second experiment, the researchers placed frogs infected with the fungus in a variety of climates. Some frogs were kept in a relatively cold environment for several weeks, with the temperature in the habitat set at 66 degrees Fahrenheit. These frogs had high levels of fungus in their bodies for several weeks. In the following months, more than half of the frogs died, Dr. Wardle said.

But the researchers found that frogs living in warmer environments, or exposed to a range of temperatures, were able to recover quickly from the infection.

With this “heat treatment,” frogs that recovered from chytrid infection were also less susceptible to future infection with the disease. Six weeks later, when they were exposed to Bd again—without the help of a warm habitat—86 percent of the frogs survived, compared with just 22 percent of the previously uninfected frogs.

Finally, the researchers tested these findings in large outdoor enclosures that more closely resembled real-world conditions. In each enclosure, the scientists stacked bricks riddled with small holes and covered each stack with a small greenhouse. Half of the enclosure exposed the greenhouse to sunlight, while the other half was shaded.

Then they placed a different species of frog in each enclosure. Some of the frogs had never been exposed to Bd before, while others were infected with the fungus or had survived a previous infection.

Both shaded and unshaded shelters attracted frogs, which took up residence in the holes in the bricks. But the scientists found that frogs in the sunlit bricks had body temperatures about six degrees higher than those in the shaded shelters. This temperature increase was enough to reduce the amount of fungus in the frogs’ bodies. “Just a few degrees of difference can make a huge difference in a frog’s body temperature,” Dr. Waddell said.

The researchers found that frogs that had previously been infected with chytrid and survived had relatively milder infections even though they did not enter the sunlit shelter.

Dr Wardle said the findings suggest that thermal refugia may act as a kind of “crude immunity”, helping frogs survive their first battle with chytridiomycosis and making them less susceptible to future infection. “You could then seed the frog population with resistant frogs and drive down population levels of chytridiomycosis.”

The strategy won’t work for every threatened amphibian – not all have heat-tracking abilities, for example – but Dr Wardle said it could be a low-cost intervention that could benefit many, and he hopes to test the approach on other frog species.

In the meantime, he is installing sanctuaries at Sydney Olympic Park, which is home to a wild population of frogs. He is also seeking public input, encouraging locals to “build frog saunas”, he said. “We’re trying to get people to put them in their backyards.

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