The fungal infection that has killed a record number of amphibians worldwide leads to deadly dehydration（脱水） in frogs in the wild, according to a new study by University of California, Berkeley and San Francisco State University researchers. High levels of an aquatic fungus called Batrachochytrium dendrobatidis (Bd) disrupt fluid and electrolyte balance in wild frogs, the scientists say, severely depleting the frogs' sodium and potassium levels and causing cardiac arrest and death.

Their findings confirm what researchers have seen in carefully controlled lab experiments with the fungus, but SF State biologist Vance Vredenburg said the data from wild frogs provide a much better idea of how the disease progresses.

"The mode of death discovered in the lab seems to be what's actually happening in the field," he said, "and it's that understanding that is key to doing something about it in the future."

The study is published online by peer-reviewed journal PLoS ONE and funded through the joint National Science Foundation and National Institutes of Health program, Ecology and Evolution of Infectious Diseases.

At the heart of the new study are blood samples drawn from mountain yellow-legged frogs by Vredenburg, who is an assistant professor of biology at SF State, and colleagues in 2004, as the chytrid（壶菌） epidemic swept through the basins of the Sierra Nevada range.

"It's really rare to be able to study physiology in the wild like this, at the exact moment of a disease outbreak," said UC Berkeley ecologist Jamie Voyles, the lead author of the study.

Unfortunately, it is a study that can't be duplicated, at least not in the Sierra Nevada. Frog populations there have been devastated by chytrid, declining by 95 percent after the fungus was first detected in 2004.

"It's been really sad to walk around the basins and think, 'Wow, they're really all gone,'" Vredenburg said.

The chytrid fungus attacks an amphibian's skin, causing it to become up to 40 times thicker in some instances. Since frogs depend on their skin to absorb water and essential electrolytes（电解质） like sodium from their environment, Voyles and her colleagues knew that chytrid would disrupt fluid balance in the infected amphibians, but were surprised to find that electrolyte levels were much lower than anticipated for the Sierra Nevada sample.