A fungal epidemic blamed for the extinction of dozens of amphibian species has drawn the attention of researchers and conservationist alike. Microbial ecologist Reid Harris and his colleagues at James Madison University in Harrisonburg, VA, say they have an idea for how to stop the spread of the chytrid fungus. The team recently identified several species of bacteria that occur naturally on the skin of many amphibians, and that inhibit the harmful effects of the fungus. Harris's research has inspired an international collaborative conservation effort, known as the Amphibian Rescue and Conservation

Panamanian golden frog Image: Brian Gratwicke

Project, which aims to save thousands of amphibian species at risk of infection by the fungus. Harris talked to The Scientist about his research and its implications for developing management strategies.

The Scientist: The Smithsonian Institution and six other zoos and institutes in Northern and Central America aim to collect $1.5 million as a part of the Amphibian Rescue and Conservation Project. What are the primary goals of this effort?

Reid Harris: In broad strokes, it's to attempt to pull out amphibians that look like they're in the line of fire of the chytrid and to rescue as many species as possible before they become extinct due to this chytrid fungus.

TS: You tested the effectiveness of these skin bacteria on the mountain yellow-legged frog, a species from the mountains of California. How did those experiments work?

RH: It was a fairly simple experimental design. The three treatments were a control, where we just added the bacteria to see what effect that had, either positive or negative, a treatment where we just added the chytrid fungus, and the one we were really interested in -- the

Cochranella euknemos (captive) Image: Brian Gratwicke

treatment where we added the bacteria first with a bacterial bath and then added the chytrid fungus. As we expected, when we just added the chytrid fungus, 80% of the frogs died, and the rest were showing signs of severe chytridiomycosis. However, when we added the bacteria first, there was no mortality at all.

TS: How do you propose to use this new information to protect wild amphibians against the fungal disease?

RH: The first step is to work with the zoos, especially the Smithsonian National Zoological Park. There are a number of different zoos that are breeding up some of these probably extinct frogs, like the Panamanian golden frog, very successfully in survival assurance colonies. The problem is you still can't let them go back in Panama in the rainforest because the chytrid is still there.

The tool we're proposing is repeating the experiment with the Panamanian golden frog that we just did with the mountain yellow-legged frog. If we get the same results in the laboratory, then we can release them into a contained environment in Panama in the field and see if the protection works in the field. This may be a tool which allows us, if the protection is long-lasting, to get these animals from the survival assurance colonies back into the field.

Horned marsupial frog (captive) Image: Brian Gratwicke

TS: What are some of the questions left to be answered?

RH: Some of the main things we want to do in the future would be transmission experiments. In other words, can we add some bacteria to ponds or soil and get transfer to the amphibians, or can amphibians transmit beneficial bacteria amongst themselves? Another question would be; What percentage of the population needs to have protective bacteria in order to prevent an epidemic outbreak? It may not have to be 100%, just like you don't have to vaccinate 100% of the human population to prevent epidemic outbreaks of various diseases -- the concept known as herd immunity. Other important questions would be, what sort of environmental effects might make the amphibians more susceptible to disease as a function of changes to their protective skin bacteria?

There are so many questions, and the urgency of this extinction crisis is so great that we urgently need more research on the microbial ecology of amphibian skin. We really just scratched the surface. The more research we can do, and not just by my research group, the better.


Related stories:

A frog's foe
[November 2008]

Frog fungus spreads in Panama
[17th October 2008]

Climate Change and Frog Deaths
[January 2008]