Boreal frogs used to be abundant in Summit County. What’s going on?

In 2018, a boreal frog was described in Summit County. Since the 1990s, a microscopic fungus has been a major factor in the decline of boreal frogs in Colorado, threatening one of the important ecological mediators of the Southern Rockies.
Liliana Wiethake/Summit Daily archive

In the past, boreal frogs thrived in Summit County’s high alpine environment, lived into their 20s, and moved across mountain passes. However, since the 1990s, a microscopic fungus has been a major factor in the decline of boreal frogs in Colorado, threatening one of the important ecological mediators of the Southern Rockies.

“It’s out of Pandora’s box,” said Valerie McKenzie, a professor at the University of Colorado Boulder who has spent years researching parasites and wildlife diseases.

According to him, the leading evidence shows that these fungi spread as a result of human activity. A foreign strain that hybridized with a local fungal strain, in turn, created a superpathogen. Wildlife officials estimate there are up to 800 wild adult frogs left in Colorado.



According to him, this decline was first observed in the 1990s, but at that time scientists could not fully understand why it happened. In 1993, Colorado Parks and Wildlife designated the frogs as endangered, and it wasn’t until 1998 that scientists officially described a fungal pathogen, the chytrid fungus Batrachochytrium dendrobatidis, that adversely affects the skin of frogs and toads. According to a study published in December 2021, this pathogen has been found in about 700 species of amphibians.

The fungus, which survives better in cold temperatures, is especially dangerous for mountain creatures and causes chytridiomycosis. Fungal exospores multiply by using skin cells as a breeding ground, bursting these cells and then spreading to more cells.



Since amphibian skin is a mucosal surface, a lot of water and electrolyte exchange takes place in their skin to keep their bodies physiologically in balance. If their skin breaks down, they can’t properly manage their hydration and electrolytes, which can lead to organ failure.

Now most of the frogs have been wiped out by the virus. Currently, there are several options for reducing the impacts of boreal frogs. One is evolution, McKenzie said, and pockets of some small species have developed natural defenses against the pathogen. There are also efforts by scientists to think about breeding amphibians with more resistance genes, but that’s easier said than done so far.

“Technologies to do this are becoming increasingly available, but understanding the genomes of amphibians is a completely different animal than understanding the genomes of humans,” he said. “When people think about gene editing for medical problems, it’s cutting edge right now. If you want to take this technology and apply it to amphibians, we’re still far behind in understanding the basics of genomes.”

This is not just a Colorado problem. According to Colorado Parks and Wildlife, amphibians around the world are experiencing alarming declines. Of the more than 3,000 amphibian species, 39% are threatened with extinction. This contrasts sharply with 10% of threatened birds or 16% of mammals. In June, teams from the Denver Zoo and Parks and Wildlife traveled to the Gunnison National Forest to introduce 570 baby frogs to wetlands that officials hope will eventually host a established population.

McKenzie said more than 50% of boreal frogs have been wiped out. What does this mean for the ecological landscape?

“To some extent, it’s very understudied,” McKenzie said. “We don’t know. It was too early to have the resources or the foresight to think, ‘OK, we’ve got to try to figure out what’s going to happen without this species out there.'”

Frogs and toads — in most ecosystems — are in the middle of the food web, meaning they eat smaller animals like insects and provide food for larger predators like foxes and birds, McKenzie said.

“Their declines give scientists early warning signs that stressors such as habitat loss, climate change, pollution and disease are making ecosystems unhealthy.” He is studying at Colorado State University. “Without amphibians, populations of insects and algae increase, which has a cascading effect on other organisms, including humans.”

If they are not as abundant species, this can lead to a trophic cascade or a series of changes in population sizes at different levels when it affects a species within an ecosystem. In addition to direct impacts, the loss of mountain frogs may also have peripheral disadvantages, such as beavers.

“If we’re removing amphibians from the entire ecosystem, it could lead to larger populations of beetles, or you could all see that these frog predators have a harder time finding food and those populations decline,” McKenzie said. . “It’s like taking out a very important intermediary in a food web ecosystem and disrupting those food web chains.”

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