Deformed Frogs - an environmental mystery

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Approximately five years ago, frogs with extra or missing limbs were first noticed in North America Hoppe; Ouellet; Souder. Initial reports came from Quebec and Minnesota but more recently such frogs have become widely distributed. Multiple species are affected with the frequency of deformities exceeding 50% in some severely affected bodies of water Hoppe; Ouellet; Souder. An important clue to the developmental pathway(s) being disrupted came from a detailed analysis of deformed frogs collected in Minnesota. One feature we consistently observed in both primary and supernumerary limbs were bones folded back on themselves. We termed these features "bony triangles" (BTs) and searched the literature for descriptions of similar phenotypes. We found that only treatment with exogenous retinoids such as RA or retinyl palmitate caused the formation of bony triangles in a variety of species. This suggested that the Minnesota frogs had been exposed to a retinoid during limb patterning. In addition, retinoid exposure could also account for hypomorphic limbs and craniofacial defects which were also prevalent in the Minnesota frogs. Visit the leglab web site for more detailed information.

We are fractionating water samples from affected sites in Minnesota and Canada to identify the agent disrupting frog development under the aegis of a STAR grant from the U.S. EPA. The materials obtained are purified to homogeneity using their biological activity (i.e., their ability to activate retinoid receptors and to disrupt development in frogs) to guide the fractionation. This unbiased approach will lead to the identification of the causative agents irrespective of their source.

Hoppe, D.M. (1997) NAAMP III online:

Ouelett, M., Bonin, J., Rodriguez, J., DesGranges, J.L. and Lair, S. (1997) J. Wildl. Dis. 33, 95-104.

Souder, W. (1996) Washington Post September 30, 1996, Page A01

Deformed frog links

Leglab - University of California Irvine
Drs. Susan Bryant and David Gardiner's laboratories study limb development and regeneration.

Minnesota New Country School
The discovery of deformed frogs in a Minnesota pond by students at this school led to a series of reports in the popular media that piqued public interest in the deformed frog problem.

Popular Literature

Bill Souder has written a series of articles about the deformed frog problem (and amphibian decline) published in the Washington Post. These are well-balanced, informative and highly recommended. Also watch for Bill's upcoming book about the deformed frogs due in Spring 2000.

In Minnesota lakes, an alarming mystery - September 30, 1996. This is the article that broke the deformed frog story in the United States.

New Reports of Deformed Frogs Trigger U.S. Ecological Alarms - January 29, 1997

Colleagues say frog deformity researchers leaped too soon - November 3, 1997.

Salamanders seem to suffer in sunlight - December 15, 1997.

A possible leap forward on amphibian abnormalities - March 16, 1998. This describes our early results implicating retinoids as a possible cause for frog deformities.

Evidence grows, suspects elusive in frogs' disappearance - July 6, 1998. Declining amphibian populations California.

Frog decline linked to climate shifts - April 15, 1999.

New suspect in frog mystery; defects feared caused by pollution are linked to parasite - April 30, 1999.

NARCAM (North American Reporting Center for Amphibian Malformations). Collection of news articles related to deformed frogs

Frog deformities linked to vitamin A. Brief article by Doug Glass of the Associated Press (March 17, 1998) describing a potential connection between deformed frogs and retinoids in the environment.

Is a New DDT Killing Frogs? - ABC News report (September 30, 1998) describing possible culprits.

Freaky Frogs, Big Mystery - ABC News report (August 7, 1998) Transcipt of Nightline report by Chris Bury outlining the essence of the story.

UV Radiation Can be Deadly - AP report (December 8, 1997) outlining possible effects of ultraviolet radiation in the worldwide decline in amphibian populations.

Yuck! Cool. And It’s Science - Deformed Frogs Introduce Pupils to the How-To’s of Research. ABC News report (April 28, 1999).


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