University of California, Berkeley and San Francisco State University researchers say their study shows high levels of an aquatic fungus called Batrachochytrium dendrobatidis disrupt fluid and electrolyte balance in wild frogs, severely depleting sodium and potassium levels, and causing cardiac arrest and death.
Lab experiments have suggested that process, but data from wild frogs provide a much better idea of how the disease progresses, researchers said.
"The mode of death discovered in the lab seems to be what's actually happening in the field," SF State biologist Vance Vredenburg said, "and it's that understanding that is key to doing something about it in the future."
The findings are based on blood samples Vredenburg and colleagues took from mountain yellow-legged frogs as the fungal epidemic swept through the basins of the Sierra Nevada range in 2004.
"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, lead author of the study.
The study will remain a one-time effort, researchers said, as frog populations in the Sierra Nevada have been devastated by the fungus, 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.