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July 6, 2009

Prof finds new cause for warped frogs

ONEONTA _ After more than 20 years studying amphibians, Hartwick College Professor Stanley Sessions has revealed another discovery about how tadpoles turn into frogs with deformities.

His early studies were about deformities caused by parasites. He responded to arguments by researchers and environmentalists about the effects of chemical pollutants. His most recent collaboration has revealed that legless frogs are the result of dragonfly nymphs taking bites of tadpoles.

Sessions and Brandon Ballengee, of the University of Plymouth in the United Kingdom, submitted their findings last year in a paper to the Journal of Experimental Zoology. Their article, ``Explanation for Missing Limbs in Deformed Amphibians,'' appeared online June 8 pending publication in its next issue, according to the journal's website.

In 1990, the same journal published Sessions' research results about frogs with extra limbs.

The findings about parasites and predatory nymphs make ``bookends'' to his work studying frogs, Sessions said during an interview last week in his office at Hartwick College.

Shelves in his office are heavy with books, photographs on the wall feature amphibians and a horse skull sits among other natural artifacts on his desk. He illustrates with his hands how a dragonfly nymph finds a meal.

Around the world, frogs have been found with missing or deformed limbs, Sessions said. Researchers studied the possible causes, and the search for answers sparked controversy and produced books on the issues, he said.

For a decade, Ballengee and Sessions have collaborated on art and science projects that show details inside amphibians' bodies. The BBC's Earth News has reported the recent findings on the dragonfly nymph. In a news release from Hartwick College, he describes the results:

"What we've found is that these predators grab tadpoles and almost surgically remove their tender hind limbs with their mandibles. They then let the tadpole swim away, and it can metamorphose into a frog that's missing a hind limb or part of hind limb. We call this phenomenon selective predation' since the predators consume only selected parts of the prey. It seems pretty obvious in hind sight, but this solves the whole rest of the problem."

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