Research: Some Wyo toads can clear themselves of deadly fungus

Tucked away in beaver ponds or under willows in northwest Wyoming live toads able to cure themselves of a deadly fungal infection.

In some ways, what the toads do is similar to how we take medicine or rest when we’re sick. Except the small population of boreal toads in the northern Wind River and Wyoming ranges hop into the sun to feel better. 

The action comes with risks — toads don’t actually like sun exposure, and open areas increase possible predation by hungry crows or coyotes — but they seem to have calculated possible death is worth it, according to new research from Gabe Barrile, a University of Wyoming doctoral researcher. 

The toads’ brethren in the Snowy Range and Sierra Madres, on the other hand, have not adapted so well. Chytrid, a deadly, non-native fungus, typically wipes out boreal toad populations in southern Wyoming, Colorado and northern New Mexico within two to three years.

Why toads in the northwest have been more successful — and how to use this news to help save amphibians — are the next big questions, researchers say. 

But first, a look at how a UW doctoral student figured out that a critter as small and elusive as a boreal toad could move to save its life. 

Invasive fungus wreaks havoc

For anyone unfamiliar with the fungus Batrachochytrium dendrobatidis, which is actually multiple strains of fungi that those outside of the scientific community often call chytrid, here’s a primer. 

Researchers believe it likely originated somewhere in Asia, though it was first identified in the late 1990s in Australia, Panama and the National Zoo in Washington, D.C. While its origins are murky, researchers do know that chytrid has spread across much of the world, said Karen Lips, a biology professor at the University of Maryland and leading expert on frogs and chytrid.

A 2019 study reported chytrid has contributed to the extinction of up to 90 species of amphibians. A relatively new study called this previous report into question. But regardless of the number of species extirpated because of an invasive fungus, even the newest report acknowledges chytrid has been devastating, particularly outside of North America. 

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Chytrid has two main stages, a sperm-like zoospore and then a zoosporangium. What they’re called is maybe less important than what they do. The zoospore floats around ponds, creeks or other water sources until it finds a host and drills into the creature’s skin. It then morphs into a zoosporangium, producing more zoospores and shoots them back into the water. Once infected, amphibian’s skin can become so saturated in fungus that the damage and reduced gas exchange contributes to organ failure. Some can live with low levels of infection, and the disease, for reasons unclear to scientists, has not been as destructive in North America as other portions of the world. But it has been documented across the country and state.

While chytrid generally thrives in cool, moist places, it does have an Achilles’ heel. It dies if it freezes or becomes too hot. 

A tale of two populations

Barrile began his work considering the catastrophic impacts of chytrid and the oddity that chytrid was causing boreal toad populations to collapse in southern Wyoming but not the northwestern portion. 

While contemplating these situations, he remembered papers about how, in laboratory settings, some boreal toads would choose to move into warmer, drier locations to “clear” themselves of the infection. 

But no one had looked to see if, in the wild, toads showed similar behavior. 

So from May 2015 until fall of 2016, Barrile and colleagues at Wyoming Game and Fish and UW’s Cooperative Fish and Wildlife Unit captured and followed almost 150 boreal toads, affixing impossibly tiny radio-transmitting fanny packs to their robust backs and testing more than 40 of them for chytrid.

The team captured and swabbed them twice a week from their breeding season at beaver ponds in spring through summer foraging and until October when they headed into their overwintering sites.

That’s when the scientists found that infected toads going into warm, dry places was likely more a survival measure than an accident. The toads that changed their environments cleared their infections. 

“It’s a brilliant adaptation to a pathogen,” said Wendy Estes-Zumpf, Game and Fish’s herpetological coordinator. 

Adapting for the future

Why the toads’ peers to the south don’t seem to be benefitting in the same way is the next question, Barrile and Estes-Zumpf said. 

It’s possible the boreal toads in Barrile’s study area are slightly better adapted to the fungus, making a brief time in the sun a useful prescription. They could have a different skin microbiome or slightly different genetics that makes them more tolerant to chytrid, she said.

It’s also possible that temperatures are higher in the lower-elevation study areas in the Wyoming and Wind River ranges versus those in southeastern Wyoming.

Scientists are now working on translating Barrile’s conclusions into possible remediation for wild amphibians. Some researchers have contemplated installing, say, heat lamps near breeding areas certain times of the year or modifying an area to create warmer, drier conditions. 

Barrile is looking at the impact of wildfire on boreal toads and chytrid. A fire 

burned through one of his study areas in the Wyoming Range in 2018, giving him the ability to compare and contrast. 

Implications of his work could extend into southern Wyoming and northern Colorado after the Mullen and Cameron Peak fires. It’s possible that as wildfires open canopies and allow more heat to reach the earth, toads could find more healing. It’s also possible the additional heat and dry conditions are as bad for toads as it is for chytrid. 

Regardless, Estes-Zumpf and others with Game and Fish will continue Barrile’s work in the Wyoming and Wind River ranges for the next few years. Boreal toads can live 25 to 30 years, perhaps longer. More data about their lives, habits and adaptability, researchers said, continues to be critical.