June 18, 2013
Fungus Spread By Bullfrogs Also Can Kill Them
April Flowers for redOrbit.com - Your Universe Online
There is currently a global decline in amphibian populations. It is believed that a major cause for this decline is a fungus thought to be spread by bullfrogs.
A two-year study from Oregon State and the University of Pittsburgh reveals bullfrogs are not only tolerant carriers that spread the disease, as previously thought. The bullfrogs are also dying from the pathogen.
The research team raised bullfrogs from eggs in controlled experimental conditions. They found at least one strain of this pathogen, Batrachochytrium dendrobatidis, also called Bd or a chytrid fungus, can be fatal to year-old frogs. The bullfrogs proved resistant to another strain of the pathogen that was tested on them.
The findings, published in EcoHealth, demonstrate that the bullfrogs are not the only culprit in the spread of this deadly fungus and add further complexity to the question of why amphibians are in such serious jeopardy.
Researchers report approximately 40 percent of all amphibian species are declining or are already extinct. Among the causes suspected are the Bd fungus, habitat destruction, climate change, pollution, invasive species, increased UV-B light exposure, and other forces.
“At least so far as the chytrid fungus is involved, bullfrogs may not be the villains they are currently made out to be,” said Stephanie Gervasi, a zoology researcher in the OSU College of Science. “The conventional wisdom is that bullfrogs, as a tolerant host, are what helped spread this fungus all over the world. But we´ve now shown they can die from it just like other amphibians.”
Bullfrogs are not actually a good host for the fungus, the study found. The fungus was first identified as a novel disease of amphibians in 1998. It is still unclear why the fungus has spread so fast, so far, and is causing such mortality rates.
“One possibility for the fungal increase is climate change, which can also compromise the immune systems of amphibians,” said Andrew Blaustein, a distinguished professor of zoology at OSU and international leader in the study of amphibian declines. “There are a lot of possible ways the fungus can spread. People can even carry it on their shoes.”
Regardless of the strain, the average infection load of the chytrid fungus in bullfrogs is considerably lower than that of many other amphibian species. The researchers found some bullfrogs can reduce and even get rid of infection in their skin over time.
The researchers concluded while some adult bullfrogs might be carriers of Bd in some areas, different hosts may be as or more important in other locations. Global pathogen distribution could be driven by the international trade of both amphibian and non-amphibian animal species.