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Resilient Spores, Tenacious Killers

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Mountain yellow-legged frogs are disappearing from the Sierra Nevada, and the culprit appears to be the resilient spores produced by the sexual reproduction of a waterborne fungus, Batrachochytrium dendrobatidis. “This group of fungi, when it reproduces sexually, creates spores that can last for a decade,” says John Taylor, professor of plant and microbial biology. This finding, which Taylor discovered through genetic analysis, means that the pathogen could be especially difficult to defeat. “As a resistant spore, the fungus can be transported by animals—including humans or birds—or it can lay dormant in an infected area until a new host comes along.”

Biologists are still determining exactly how this fungus, first identified in 1998, kills the amphibians it infects, but most believe that the pathogen disrupts the frog’s ability to absorb water through its skin. Tens of thousands of mountain yellow-legged frogs in hundreds of Sierra Nevada sites have disappeared in the wake of the pathogen’s emergence.

While the U.S. Fish and Wildlife Service considers listing the mountain yellow-legged frog as an endangered species, biologists are racing to find ways to halt the spread of the frog-killing fungus.

“This frog used to be the most abundant amphibian, perhaps even the most abundant vertebrate, in the whole Sierra Nevada,” says Taylor. “Over the past 30 years, it has disappeared from almost 95 percent of its historic range, and its absence is impacting other organisms. Garter snakes that used to prey on these frogs are now declining as well. The frog’s disappearance is leading to the unraveling of a high-elevation ecosystem.”

-Sarah Yang

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