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Love in the Time of Chytrid

Written by Brittany A. Mosher is a 2016-2017 Sustainability Leadership Fellow and Ph.D. Candidate in the Department of Fish, Wildlife, and Conservation Biology.

It’s a tale as old as time. A gal shows up at a local watering hole, feeling hopeful and excited. She’s kissed a lot of toads in her day, which hasn’t been all that bad, but she is still looking for her prince. As the minutes slowly turn to hours, the exhilaration turns to dread. “This can’t be happening”, she thinks to herself. But the longer she waits, the more certain she is that it is happening. This time, like the last, she has been stood up.

In this day and age, toad love is tough love. At a stunning wetland at 11,000 feet in elevation a lovely female boreal toad named Anura has been stood up. And she hasn’t been jilted by just one particular toad with commitment issues. No, she has been abandoned by every male toad.

In late May in the high country of Colorado the snow is just starting to melt. Two days ago Anura made her way out from under the cozy log where she spent the last seven months, and began the kilometers-long trek across the frozen ground to the same wetland where she was born. She’ll wait several days for a mate, but just like last year, she is the only member of her species at the pond. The only visitors she has are human researchers who study declining boreal toad populations.

We, as researchers, are just as confused as Anura is. Boreal toads in Colorado are in trouble, in large part due to an invasive chytrid fungus. Chytrid is responsible for toads vanishing at this wetland and at many others in Colorado. We didn’t expect to find any toads at the pond during this visit. Several years ago, we placed an electronic tag in Anura’s body so that we could identify her, the same way that a veterinarian embeds a microchip in a beloved pet. This year when we scan Anura—like a box of cereal at the supermarket—her unique code pops up. We are shocked to find that this is the same lone female we found here last year.

Why are we so surprised? Last year, Anura’s skin tested positive for chytrid. In toads like Anura, chytrid often carries a death sentence, and we did not expect to see her again. The fact that she made it through the long winter without succumbing to disease makes us wonder if she may carry a form of genetic resistance. It’s heartbreaking that she may not have a chance to mate again, because her genes could be crucial for the survival of this species.


A tiny terror

Chytrid spores swim in water and burrow into the skin of amphibians (frogs, toads, and salamanders) that they encounter. Amphibian skin is like a dish sponge – porous enough that oxygen and moisture can be absorbed. The skin also teems with bacteria that helps amphibians stay healthy. An amphibian whose skin is taken over by chytrid often becomes lethargic, stressed, and can die of a heart attack. So far, chytrid has been related to population crashes of over 200 amphibian species all over the world, including the boreal toad.


With many amphibian species in decline in Colorado and around the globe, captive breeding programs, reintroductions, and translocations have become necessary management actions. Researchers at Colorado State University are teaming up with agencies like Colorado Parks and Wildlife and the National Park Service to learn more about boreal toads and to use research to help make decisions about how to conserve these increasingly rare species that are an important part of healthy ecosystems.

Generally, we find chytrid by capturing toads at wetlands and swabbing their bodies with cotton swabs. Back in the laboratory, we search for chytrid spores on the swabs. If we find the spores, we know that chytrid is present at the wetland and that boreal toads are likely to be in danger. Sampling for chytrid has gotten more difficult as toads have become rarer. Many of the beautiful places once brimming with amorous, chirping toads in the early summer are now silent, with few or no representatives of the species.

Conservation in action

One strategy to restore toad populations is to reintroduce boreal toads raised in captivity to these depleted wetlands where toads no longer roam. But what if chytrid is still living in the water, waiting for its next opportunity to attack? I study how to sample chytrid in pond water before reintroduction events, without needing to catch toads or other amphibians. By pumping pond water through very small filters, chytrid spores that get “caught” can be identified. These filters can help our collaborators find wetlands without chytrid where boreal toad reintroductions might be successful. The data can also give information about how much chytrid is in the water at different sites so that conservation biologists everywhere can learn what kinds of ponds are least hospitable to chytrid. When I was a youngster in upstate New York, far from the toads of Colorado, my father and I would sit on the porch in the early spring and wait to hear the sound of frogs calling. For me, that melody was the first indication that the land was thawing and that summer would come, bringing along with it all of the good things that children look forward to. I didn’t know that I’d someday spend several years of my life trying to understand what was happening at the now silent ponds of Colorado.

A plan for recovery

While this chapter in the book of boreal toads is a sad one, the story isn’t over yet. A group of state, federal, and non-profit wildlife agencies in Colorado (known as The Boreal Toad Recovery Team) is pooling resources and sharing data to make decisions about how best to manage existing boreal toad populations and to create new ones. In California, a frog that was in decline in part due to chytrid has started to recover. And in Colorado, several reintroductions have been attempted and our first success story has emerged: a brand new toad population at a pond without chytrid. With a little help from conservation biologists, these mountain residents may once again find love at our mountain ponds.

Get in touch with Brittany A. Mosher to talk toads! @BAMdoesscience


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