A dramatic increase in deformed frogs and other amphibians is being caused by a range of environmental factors, all of which ultimately can be linked to human impacts on habitat, but the primary cause of many of the deformities is an epidemic of a key parasite.
These findings are the results of eight years of research by scientists around the world, and are presented in the February issue of Scientific American by researchers from Oregon State University and the University of Wisconsin.
The cause of a disturbing increase in amphibians with deformities are explored in a new article in Scientific American by researchers from Oregon State University and the University of Wisconsin. Extra legs, such as those found on the frogs in these images, are one of the most common deformities.
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According to the researchers, the story of the parasitic trematode reveals just how complicated natural ecological processes can be, and how difficult it is to trace problems to their underlying cause. In its life cycle, the parasite at times depends on snails for survival and birds for reproduction and transportation. The amphibians, themselves, are actually just an intermediary host.
"We need to understand the complex relationships among human activity, the parasite and its hosts, and the environment in which they interact," Johnson said.
There are many interrelationships among various factors. Snails, for instance, are necessary to the life cycle of the trematode that can cause frog deformities. But snail populations may be surging at some sites due to fertilizer runoff and cattle manure that cause algal blooms and more food for the snails. A survey of the western U.S. in 2000 found that 44 of the 59 wetlands in which amphibians were infected by this parasitic trematode were reservoirs, farm ponds or other artificial bodies of water.
And water pollutants or UVB radiation, while not directly causing the majority of deformities, may set the stage by weakening an amphibians immune system and making it more vulnerable to a parasitic infection.
"The challenge to scientists becomes teasing apart these agents to understand their interactions," the researchers said in this article. "Humans and other animals may be affected by the same environmental insults harming amphibians. We should heed their warning."
Andrew Blaustein | EurekAlert!
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