University Times

They were the first vertebrates to crawl out of the primordial soup and live on the land 350 million years ago. But these seemingly hardy souls, the amphibians – frogs, toads and salamanders – are dying off at alarming rates. And no one is sure why.

Like canaries in a coal mine, amphibians are one of nature’s best indicators of overall environmental health since their highly permeable skin is sensitive to changes in water and air quality.

At least 32 percent of all known species of amphibians are threatened by extinction, according to the recent World Conservation Union study, the Global Amphibian Assessment, the most comprehensive study ever of amphibian populations conducted by more than 500 scientists from over 60 nations.

“The latest evidence suggests that amphibians are declining faster than other groups are. They may be a first sign that things are not going well,” according to Pitt biologist Rick Relyea, who has been studying the impact of pesticides on amphibians.

“If you imagine this problem globally, there isn’t just one cause,” he said. The most obvious hazard amphibians face is development: Roads, towns and agriculture drain and plow over prime amphibian prime habitat — standing water. And there are a host of other, often more localized causes for decline. Different habitats have different problems: A fungus in Central America and ultra-violet rays in the northwestern United States are threatening those native amphibian populations. Let’s not forget the impact of invasive species: Trout transplanted to Rocky Mountain ponds for recreational fishing wipe out the amphibians there. “They eat them like crazy,” Relyea said. And the American bullfrog, an eastern U.S. native that made its way out west, has overpowered smaller species of frogs and toads, taking their food. The native amphibian population is further assaulted when the adult bullfrogs eat their tadpoles.

And then there are pesticides, historically a problem. The most famous example is the effect of DDT that brought the bald eagle to the brink of extinction in the late1970s. Is there some other chemical playing more havoc than realized? It’s hard to tell, according to Relyea, because of the approximate 80,000 registered chemicals tested by the Environmental Protection Agency or manufacturers, none of them are tested for damage to amphibians. “You have to test a bird, mammal, a fish and a crustacean – these guidelines have been in effect for decades, long before people cared about amphibians,” he said. “And it could be difficult to change testing now: If you have a history of testing the first 20,000 chemicals with these four groups of animals, then it makes sense to test all other things against that.”

Instead, the scientific community is learning more about pesticide impact from researchers like Relyea, who came into the field as an ecologist with a background in how amphibians reacted to stress. And in nature, stress most always translates into who is going to eat whom. Under stress, tadpoles will change color, change shape. And amphibians can smell danger: When a predator such as a salamander or a dragonfly urinates or defecates, tadpoles can detect the type of predator and what it has eaten.

Relyea’s recent research explores the pesticide connection. “The mystery is, why would amphibians decline in a place that has pesticides but they are at low concentrations?”

He set up experiments similar to ones done by the EPA for other wildlife, but he extended the tadpole’s exposure time to an insecticide and introduced stress. “In one of our recent papers, we showed that 2 percent died with the pesticide while 92 percent died with pesticide and smell of predators. So it became 46 times deadlier that anyone ever knew. And no one had ever done this experiment with any animal before.”

Relyea’s work might provide a clue as to why amphibians are declining in pristine areas such as the Rocky Mountains. From California’s central valley, heavy with agriculture, the wind can carry scant amounts of pesticides to the Rockies. “We think one good guess is that the human impacts – such as pesticides and pollution — are being carried on the wind.” Given that the stress of predation coupled with pesticides nearly wipes out the population of tadpoles in the laboratory, Relyea would like to take his research to a more natural situation. “Can we build real ponds and treat them with pesticides and ask what happens to the whole community, not just the frog. Can we do this long-term?” Well, Relyea will work on those question this spring at Pitt’s Pymatuning Lab of Ecology, where he already has set up 400 artificial ponds.

-Mary Ann Thomas