Yosemite toads face high fungus infection rates after winter

A study published in Functional Ecology reveals that young Yosemite toads are highly vulnerable to the deadly chytrid fungus, Batrachochytrium dendrobatidis (Bd), during their first winter underground. Researchers found that while approximately 23 percent of juvenile toads tested positive for the fungus before entering winter burrows, infection rates surged to over 90 percent upon their emergence in the spring.

The fungus is waterborne and attacks amphibian skin, disrupting essential electrolyte and fluid regulation, which frequently leads to fatal heart failure. This pathogen is a significant driver of global amphibian declines and is a factor in the Yosemite toad being listed as threatened under the U.S. Endangered Species Act.

Ecologists, including David Daversa from UCLA, noted the mystery of how a water-loving pathogen thrives in subterranean burrows beneath feet of snow in the Sierra Nevada mountains. To mitigate these risks, conservation efforts by the San Francisco Zoo and the U.S. National Park Service have shifted toward releasing mature toads that have already passed these vulnerable early life stages.