Yosemite Frogs Jump Back from Fungus Attack

Some good news on the wildlife conservation front: the Sierra Nevada yellow-legged frog (Rana sierrae), an endangered amphibian that has faced near-extinction, is showing signs of recovery in Yosemite National Park.

Once abundant in the high-elevation lakes and streams of California’s Sierra Nevada mountains, the species suffered dramatic declines due to habitat changes and a lethal fungal disease.

A new study, published in Nature Communications, details a 15-year effort to reintroduce frogs from disease-resistant populations into areas where they had been wiped out. The project, which spanned from 2006 to 2020, has seen encouraging results, with most reintroduced populations reproducing and establishing footholds in the wild.

The Challenge: A Lethal Fungus

The chytrid fungus (Batrachochytrium dendrobatidis, or Bd) has decimated amphibian populations worldwide, causing mass die-offs and driving many species to extinction.

The Sierra Nevada yellow-legged frog, one of a dozen amphibian species found in Yosemite National Park, was already struggling due to habitat disruptions like the introduction of non-native fish, was particularly vulnerable. The spread of Bd in the mid-20th century caused over 90% of its population to disappear.

However, researchers found that some frog populations had survived Bd outbreaks and appeared to develop resistance. These resistant populations became the foundation for the reintroduction effort.

A Slow but Promising Recovery

Between 2006 and 2020, scientists translocated frogs from these surviving populations to 12 sites in Yosemite. Of the reintroduced populations, nine showed consistent signs of reproduction, with tadpoles and juvenile frogs observed year after year.

Population models used in the study suggest that many of these reintroduced populations are likely to persist for at least 50 years, assuming current conditions hold. The findings indicate that resistant frogs can sustain populations even in environments where Bd remains present.

While not every translocation was successful, the study’s authors noted improvements in survival rates over time as they refined their methods, such as selecting higher-quality habitats for reintroductions.

Implications for Conservation

The rebound of the Sierra Nevada yellow-legged frog highlights the potential for targeted interventions to support species struggling with disease and habitat loss. However, challenges remain. The continued presence of Bd, combined with the long-term pressures of climate change and habitat disruption, means that the future of the species is not guaranteed.

Restoring the frog across its historical range will require significant effort, according to the study’s authors, including habitat protection and ongoing monitoring. Additionally, the study underscores the importance of understanding and working with natural processes, such as disease resistance, in conservation strategies.