Imperiled tropical frog shouting the impact of climate change from the mountaintops

The frog species, known as the mountain coqui to the hikers they serenade at night and Eleutherodactylus to researchers, has for decades battled a lethal fungus to a standstill, says Ecology and Evolutionary Biology Professor Kelly Zamudio. The coqui populations endure the drier winter months when stress makes them vulnerable to the imported fungus Batrachochytrium dendrobatidis, or Bd, then rebound when the wet season returns to their tropical forest home.

But now, climate change may be tipping the balance in this biological standoff.

Zamudio, whose lab is looking into climate change and disease with the support of the Academic Venture Fund administered by the Cornell Center for a Sustainable Future, has teamed with graduate student researcher Ana Longo. During her master's degree work at the University of Puerto Rico, Longo followed how climate change altered weather patterns in the Caribbean. She found that periods of drought during the winter months from December through April have grown longer, with rainless spans once rarely longer than three days now stretching up to nine or 10 days. That puts the coqui under added stress, and stressed frogs are less likely to survive when Bd comes calling. To make matters worse, the frogs sometimes retreat at "clumping sites" to ride out the droughts, helping spread the fungus among weakened populations.

"It's like a train wreck," says Zamudio, who noted that Bd is responsible for almost half of the 190-plus frog species extinctions observed in the past half century.

In the next phase of the work through Zamudio's lab, Longo will return to Puerto Rico in January 2011 examine whether climate change is undermining one technique the frogs use to battle the fungal infections. Called "behavioral fever," the ectothermic, or cold-blooded, frogs use their environment to elevate body temperature and battle disease. Now, it seems that longer and less predictable winters driven by climate change may be stripping the frogs of this defensive tool as well. Zamudio and Longo said their goal is to understand this two-pronged threat to the coqui in the mountains of Puerto Rico, because other tropical frog species throughout Central and South America are showing the same infection patterns.

"If we lose these frogs, we lose a link in the food chain," Zamudio says, "and that has community consequences for entire ecosystems."