Complicated Efforts to Save Frogs

Complicated Efforts to Save Frogs

Aug. 2007  – A deadly fungus that has 
wiped out mountain yellow-legged frogs across California's Sierra Nevada 
can spread by sexual reproduction, complicating efforts to save the frogs 
from extinction, finds a new genetic analysis from the University of 
California-Berkeley. 
Once the most abundant amphibian in the Sierra Nevada, tens of thousands 
of mountain yellow-legged frogs have died at hundreds of sites over the 
past 30 years.
  
Scientists have attributed these deaths to chytridiomycosis, a quickly 
spreading disease caused by the waterborne fungus, Batrachochytrium 
dendrobatidis. But the deaths have also been blamed on the introduction of 
non-native predatory fish. 
Set for publication next week, the study suggests that the fungus played a 
bigger role than the fish because of its ability to spread over long 
distances and persist in the environment through sexual reproduction. 
"This group of fungi, when it reproduces sexually, can create spores that 
can last for a decade," said John Taylor, UC Berkeley professor of plant 
and microbial biology and principal investigator of the study. "That could 
make this pathogen a harder problem to defeat." 
The fungus can be spread by people who transfer the spores around the 
world in dirt on shoes or car tires, warns the study's lead author Jess 
Morgan. Spores also can be carried across mountain ranges by birds. 
Exactly how this fungus kills the frogs it infects is still unclear, but 
most scientists believe it disrupts the skin's ability to absorb water. 
As the U.S. Fish and Wildlife Service considers listing the mountain 
yellow-legged frog as endangered, biologists are racing to stop the 
spreading fungus. 
First identified in 1998, the fungus has moved across the Sierra Nevada at 
about a mile per year. 
The UC-Berkeley study could help explain the global spread of this fungus, 
which has been found in South America, Australia, Europe and Africa even 
in remote, pristine areas.

"Up until now, people thought the movement of this pathogen was mainly via 
infected frogs, so such measures as restrictions on the pet trade were put 
in place," said Morgan, a UC-Berkeley researcher during the study and now 
a government scientist in Queensland, Australia. 
Study co-author Roland Knapp, an ecologist at UC Santa Barbara's Sierra 
Nevada Aquatic Research Laboratory, has tried to reintroduce mountain 
yellow-legged frogs in remote lakes in Sequoia and Kings Canyon national 
parks and the John Muir Wilderness where previous frog populations had 
been wiped out. 
Out of 10 reintroduction attempts, seven have failed. 
"Within two years, the healthy frogs we introduced would become infected 
with the fungus and die," said Knapp. "It's a stunning thing to see. One 
year, there is no obvious evidence of the disease, the next year, we'd 
come back to see hundreds of dead or dying frogs, and then the following 
year, they'd all be gone." 
"Garter snakes that used to prey on these frogs are now declining," said 
Knapp. "A high-elevation ecosystem is unraveling." 
The study appears in next week's issue of "Proceedings of the National 
Academy of Sciences." 

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