Frog Fable #1 - Frog Disease is Spread by Researchers

Due to an extremely busy summer field season, it has been several months since I've had the luxury of a few days off. As regular readers have surely noticed, that lack of time has seriously limited my ability to continue with my usual weekly posts. But now, with fall in the air, my field season has concluded and I can once again return to a more sane schedule. So, you can look forward to weekly posts once again.

As an ecologist involved in efforts to restore mountain yellow-legged frog populations, I have the opportunity to read lots of comment letters submitted by members of the public in response to various frog-related agency projects. These letters are an important part of any democratic process, but some of the statements contained in these letters take undue liberty with the facts as we currently understand them. Given my firm belief that sound decisions designed to conserve biodiversity (and mountain yellow-legged frogs in particular) absolutely depend on decision-makers and the general public understanding the current "state of the science", I'll use my next several blog posts to clarify some of the most common misunderstandings.

As detailed on the Mountain Yellow-legged Frog Site, chytridiomycosis (the disease caused by the amphibian chytrid fungus, Batrachochytrium dendrobatidis) is associated with declines and extinctions of amphibians all around the world. Mountain yellow-legged frogs are highly susceptible to this disease and many recent disappearances of frog populations in the Sierra Nevada are attributable to chytridiomycosis outbreaks (click here for details). Some people, perhaps concerned that the steady decline of the mountain yellow-legged frog will result in calls for additional removals of nonnative trout, have sought to pin the blame for this decline on the scientists studying the problem. Scientists, the argument goes, have been spreading the chytrid fungus from frog population to frog population during the course of their research.

On the surface, this seems a reasonable argument but it ignores several important facts. First, research in Australia, Central and South America, and California's Sierra Nevada indicates that the chytrid fungus is spreading as a distinct front and is moving into new areas at a very predictable rate. This uniform spread is not what would be expected if researchers (whose movements could perhaps best be described as haphazard) themselves were the agent of spread. Second, in the Sierra Nevada and elsewhere chytridiomycosis has spread into many areas that were never visited by amphibian researchers. And third, amphibian scientists around the world (including those of us working in the Sierra Nevada) adhere to a strict protocol of chemically disinfecting all of their field research gear between each visited water body or watershed.

A far more likely vector of the chytrid fungus is infected frogs moving between water bodies. In addition, adult stages of aquatic insects fly in great numbers from one water body to the next, and could be effective agents of disease spread. The half-baked notion that researchers themselves are spreading the amphibian chytrid fungus provides a convenient scapegoat but it doesn't hold up under even the most basic scrutiny.

Next week I'll discuss the common misconception that the discovery of the important role played by the amphibian chytrid fungus in causing mountain yellow-legged frog declines exonerates nonnative trout as a major cause of these declines.

Back to The Mountain Yellow-legged Frog Site.