This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: UCLA biologists have found the hiding place of a silent killer stalking threatened Yosemite toads: their own burrows. The Batrachochytrium dendrobatidis (Bd) fungus decimating amphibian populations around the world has long been thought to live in and infect the toads through their skin when they are in the water.
However, the researchers discovered a high infection rate in previously healthy toads when they emerged from winter hibernation, suggesting that the fungus proliferates in their underground burrows during the harsh Sierra winter. The finding has informed a captive-rearing and reintroduction program at Yosemite. "The results of our Bd surveillance study of Yosemite toads were completely unexpected," said UCLA ecologist Dave Daversa, the first author of a paper published in Functional Ecology.
"Although Bd is a largely aquatic pathogen, we discovered that major outbreaks of infection grow and spread during winter hibernation on land. The discovery sharply contrasts with current thinking about the high-risk season for Bd infection, which has often been assumed to occur when amphibians are breeding in water. Our study flies in the face of that expectation." The Yosemite toad (Anaxyrus canorus) lives almost exclusively in Yosemite and in Sequoia and Kings Canyon national parks.
They are only about 1 to 3 inches (2.5 to 7.6 centimeters) long and walk, rather than hop. Females are larger than males and have bumpy skin mottled attractively in varying shades of green, while males are less colorful. They breed in small pools but spend much of their time chilling (literally) and hiding from predators in abandoned rodent burrows.
The toads survive harsh winters in the High Sierra by hibernating in their burrows. But climate change is making their habitats drier and hotter, and fewer tadpoles are growing to adulthood. Infection with Bd—which is fatal—is widespread.
As a result, the Yosemite toad was listed as threatened under the Endangered Species Act in 2014 and by California as a highest-priority species of special concern. The toads were being reared at the San Francisco Zoo and returned to the wild to restore the population, but it wasn't known how Bd might be complicating these efforts. From 2021–2023, a group of researchers from UCLA and Yosemite National Park surveyed toads to determine how Bd prevalence and severity varied across seasons and life stages, comparing them before and after cohorts of toads entered winter dormancy.
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