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> February 18, 2000:
Hour Two: Amphibian Decline
| Several years ago, a group of students in Minnesota called attention to the problem of deformed amphibians. After the students noticed an unusual number of frogs with misshapen, missing, or multiple legs, others soon began to report similar sightings. Concern began to spread. | 
A 6-legged leopard frog. NPS image. |
At the same time, biologists and ecologists were puzzling over another threat facing frogs, toads, and salamanders. Populations of some species of amphibians were seen to be declining without explanation. A species of gastric brooding frog was discovered in Australia but then disappeared -- and is now thought to be extinct. Other dramatic declines, such as the dieoff of a species of golden toad in Costa Rica, also called attention to a mysterious threat facing world amphibian populations.
Scientists aren't sure what's causing the population declines, or the deformations. Indeed, the two problems may not even be linked. While some people have suggested that chemical pollutants from human sources may be to blame, not all the evidence points to humans as the direct culprit. Although pollutants might concentrate in wetland habitats, many of the amphibian declines have occurred in remote, relatively unspoiled areas with limited human contact.
There are many potential causes. Exposure to ultraviolet light (UV-B) has been suggested as one. Ultraviolet radiation could harm amphibian eggs, or increase an amphibian's susceptibility to attack by a fungus or disease. A chytrid fungus has been tied to a dieoff of frogs in Colorado. A salamander dieoff in Utah was tied to a viral outbreak. And several scientists have pointed to a type of parasite called a trematode as a potential cause of the deformed amphibians.
Amphibian physiology may make them especially sensitive these problems. Amphibian eggs generally mature in water, where they may be exposed to chemical or biological threats. In addition, delicate amphibian embryos lack a hard, protective shell to protect them from hazards. Furthermore, their highly permeable skin, adapted to allow gases and moisture to pass in and out, could be equally accommodating to disease-causing factors.
 USGS image | What might the problem be -- and what is being done about it? On this hour of Science Friday, live from the annual meeting of the American Association for the Advancement of Science in Washington, DC, we'll talk about the decline in amphibian populations around the world, and share your comments and questions with our panel of expert guests. Be sure to tune in. |
Guests:
James Collins
Professor, Biology
Arizona State University
Tempe, Arizona Cynthia Carey
Professor, Biology
University of Colorado
Boulder, Colorado Andrew Blaustein
Professor, Biology
Oregon State University
Corvallis, Oregon Karen Lips
Assistant Professor, Zoology
Southern Illinois University
Carbondale, Illinois
Books/Articles Discussed:
| C.Carey, N. Cohen, and L. Rollins-Smith (1999). "Amphibian declines and disease: an immunological perspective." Devel.Comp. Immunology 23/; 459-472.
C. Carey (2000) "Infectious Disease and World-wide Declines of Amphibian Populations..." Environ. Health Perspect., 108,Suppl. 1:1-8.
| | Related Links:
Amphibian Malformations
NBII - FrogWeb Homepage
USGS - BRD - NWHC's Home Page
Summary of Declines in Amphibians
12-08-97 Field study links sunlight to amphibian deformities
Frogwatch USA - USGS Patuxent Wildlife Research Center
Frog Home Page
Welcome to the NAAMP
DAPTF Home Pages
- This segment produced by:
Annette Heist
Web producer:
Charles Bergquist |