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Amphibian Researchers Face New Fungal Fight

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The hard-won lessons from a fungal epidemic that has killed millions of frogs around the world might help save salamanders and newts from a new fungal threat, researchers said at a 11 February press briefing at the 2016 AAAS Annual Meeting.

More than 200 species of amphibians have become extinct or near extinct as a result of infection by the fungus Batrachochytrium dendrobatidis or Bd, making it one of the most devastating wildlife diseases ever recorded.

It took years for scientists to connect Bd to frog extinctions, but when a new fungus called Batrachochytrium salamandrivorans or Bsal began infecting salamanders in the Netherlands in 2013, researchers identified it as a lethal threat within 10 months. Amphibian researchers, concerned that Bsal could invade North America next, helped to convince the U.S. Fish and Wildlife Service to ban the importation and interstate transport of 201 salamander species in the United States. The ban, mostly aimed at salamanders imported as part of the pet trade, went into effect in January.

The ban was critically important to scientists like Vance Vredenburg, a San Francisco State University amphibian biologist who advocated for the move in a 2015 Science paper. In his own research on Bd frog extinctions in California, "I saw tens of thousands of animals die right in front of my eyes in the most pristine environment you can imagine," he said. "We've come a long way in the last 20 years, and now we're trying to apply the lessons learned from Bd to Bsal."

Karen Lips (l), Ana Longo, Patricia Burrowes and Vance Vredenburg speak at the 2016 AAAS Annual Meeting. | Boston Atlantic Photography

Those lessons include learning more about the genetic makeup of Bd, how and when the fungus spread to infect amphibians on every continent except Antarctica, and how the amphibians fight back against the fungus.

Karen Lips, a University of Maryland biologist who was one of the first to sound the alarm on frog die-offs in Panama and Costa Rica, said that researchers now know that Bd isn't a single fungus, but a suite of at least six distinct genetic variants "with different virulence for different amphibian species."

Lips and University of Maryland postdoctoral fellow Ana V. Longo said that global collaborations between amphibian researchers have been key to understanding Bd's diversity. These collaborations also showed that some frogs are more susceptible than others to Bd infection, in part because they mount different immune responses to the fungus. "We expect to find more of this same diversity in Bsal," Longo noted.

Dr. Joseph R. Mendelson of Zoo Atlanta displays a variety of amphibians.| Boston Atlantic Photography

Researchers including Patricia Burrowes of the University of Puerto Rico have studied the connection between environmental conditions and Bd virulence, concluding that climate factors can have a significant impact on frog infections. On a global scale, the fungus thrives in areas with low temperatures and high humidity. At a more local level, Burrowes says, the prevalence of Bd can be affected by how frog species migrate, and regional climate conditions such as drought could drive some frogs to clump together at a few humid spots and increase their risk of infection.

Lips said scientists have learned more about how the amphibian extinctions can have "big impacts on all parts of an ecosystem." In her Central American field sites, for example, she saw everything from changes in water quality to a surprising number of starving snakes when the frogs began to disappear. "We don't know yet if we can get these places back to their original state," she said.

The missing frogs have created cultural disruption as well, Burrowes said. In places like the Caribbean island of Dominica where the massive mountain chicken frog has nearly disappeared as a result of Bd infection, the islanders have lost a valued source of meat and a local festival thrown in honor of the amphibian.


[Credit for related teaser image: Boston Atlantic Photography]