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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