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Microscopically Going Where No One Has Gone Before

Photo by Monty Rand

Microscopically Going Where No One Has Gone Before
UMaine mycologist plays critical role in investigations of amphibian die-offs worldwide

About the Photo: "Frogs are an integral part of the ecosystem. To have species go extinct is a terrible thing." —Joyce Longcore

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In the summer of 1997, a successful project to raise blue poison dart frogs hit a snag at the Smithsonian National Zoological Park in Washington, D.C. During metamorphosis, the change from tadpole to frog, the amphibians native to South American rainforests were dying of unknown causes.

The only clues were spherical bodies inside the skin cells of the dead animals.

The search for answers led the zoo's veterinary pathologist to University of Maine mycologist Joyce Longcore, one of the few scientists in the world who studies the Chytridiomycota (known as chytrids), a type of aquatic fungi.

"As soon as I saw the photographs, I knew (the culprit) was a chytrid," says Longcore. "I had spent the last 10 years isolating chytrids and growing them in pure culture. The blue poison dart frog was the first (amphibian) from which I isolated this particular chytrid, then we showed that it is capable of causing disease and death."

The same summer, scientists in Australia found the organism decimating populations of species in the wild. In addition, a researcher doing frog surveys in Central America one year returned the next year to find the rainforest eerily quiet and frogs dead along the streams.

"The scientists didn't know what the disease organism was at the time; now we know it was a chytrid," she says.

Longcore is quick to point out that she is not looking for the cure. Yet she is key to the investigation because she is providing invaluable chytrid cultures that other scientists need for experimental research.

Aquatic fungi are everywhere — in water and soil, even in the rumens of cows. Yet aquatic fungi have been little studied because, as microscopic parts of the ecosystem, they seemed to have little economic importance. But with the increase of aquatic agriculture, and deaths of amphibians in captivity and the wild, aquatic fungi like chytrids are increasingly under the microscope.

"When we first found it, we thought the chytrid would kill all it infected. Now we know it doesn't," Longcore says.

With National Science Foundation funding, researchers across the country are collaborating with Longcore and using her cultures to study the systematics, taxonomy and phylogeny of chytrids. She also is training a new generation of researchers to pick up where she will leave off in isolating cultures.

Longcore started isolating chytrids into pure culture in the mid-1980s. Now with more than 300 isolates, 80 of them of the chytrid pathogen from frogs and toads found in California, Colorado, Wisconsin, Quebec and Maine, she has the most comprehensive collection of the chytrid phylum in the world.

"I isolate cultures so someone else can use them and determine answers to the big questions," Longcore says. "For me, the thrill is in going microscopically where no one else has gone before."

Throughout the Northeast, and especially in Maine, Longcore has studied frogs and toads, and found the "frog chytrid" statewide.

The big questions have to do with what the deaths mean environmentally and ecologically. Are frogs that are dying of chytrids harbingers of a yet unseen shift in the ecosystem, much like a canary in a coal mine? Or is this an invasive disease that has spread from a different continent?

Longcore predicts that in 10 years, we'll understand where the chytrid that attacks amphibians came from and how it is distributed. Perhaps that will help us prevent die-offs.

by Margaret Nagle
February-March, 2002

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