Malformed Amphibians

© 1998 Minnesota Pollution Control Agency

Headlines in two Minnesota (US) Newspapers told the story: "Deformed frogs prompt investigation--Students found large numbers of them in Henderson" (Minneapolis Star/Tribune, 9/1/95) and "Leap in Frog Mutations Startles Scientists" (St. Paul Pioneer Press, 9/1/95). In 1995, students in Minnesota alerted the world to the problem of frogs with unusually high numbers of malformities. Some frogs had up to five hind legs, some had unusual webbing or missing legs, and some were missing eyes. These trends have continued with some more extreme malformities even being found.

(These photos of a frog with an extra leg were mailed from a family living in a suburb of the Twin Cities.)

Because frogs may act as bio-indicators of the health of our environment, scientists began to worry. As with global amphibian declines, suggested causes for these malformities include increased exposure to ultra-violet light, chemical contamination (both have been related to human activities) and parasites.

Judy Helgen, a research scientist with the Minnesota Pollution Control Agency (MPCA) became involved with the students and their teacher Cindy Reinitz in trying to solve the problem. She began to wonder what else we might find if we looked in our back yards. She thought that thousands of youth could help look after the health of our amphibian friends. The seed for this project had been planted!

When the project began, A Thousand Friends of Frogs has passed information from citizens onto research scientists at the MPCA concerning the malformed frogs and toads. To find out about the results of the survey in Minnesota, click here. Reports are also passed to the North American Reporting Center for Amphibian Malformations. To find out more about the data available, click here.

The MPCA is also working closely with the National Institute of Environmental Health Sciences (NIEHS) (Research Triangle Park, North Carolina) trying to determine the cause of this phenomenon.

Click here to read the latest news on frog malformities.

What is the difference between
a deformation and a malformation?

Deformation is the process of disfiguring a part of the body that already exists, while malformation is the process of disrupting a normally formed organ or body part during the original stages of development. Most of the abnormalities we are addressing are really malformations even though many people refer to them as deformities.

What Scientists are saying about
Amphibian Malformations in Minnesota

Is the problem with ultra-violet light?

The earth is protected by a layer of the invisible gas ozone; this is the ozone layer, and it does a great job of filtering out harmful rays of ultra-violet light from the sun (visible light is what plants use to make sugar, in the process of photosynthesis). However, some chemicals produced by humans called chlorofluorocarbons--or CFCs for short--dissolve or thin the ozone layer when they are released into the air. CFCs were used in air conditioners, refridgerators and some aerosol (spray) cans but have now been banned. However, they can affect the ozone layer for many years. Scientists warn us that these CFCs have made a thinned the ozone layer, particularly over the south pole, but the ozone layer is getting pretty thin over the northern half of the earth as well.

As we lose our ozone layer, we also lose some of our protection from ultra-violet light. In humans, harmful ultra-violet--or UV--rays have been proven to cause cancer, especially skin cancer, and can lead to eye problems such as cataracts. Our concern about UV light has lead us to be careful about wearing sunscreen and sunglasses, now more than ever.

What does this have to do with frogs?

In a laboratory study in Duluth, MN, in late 1997, almost half of the frogs that were exposed to UV rays as eggs had malformed legs, while in a control group--no UV exposure--none of the frogs were malformed. There is also evidence that UV light levels are highest in late spring and early sumer, when Minnesota's frogs are actively laying eggs. More research still needs to be done to see what UV does to frog eggs in natural environments. It is still too early to say whether UV light is completely, or even partly, responsible for the frog malformities seen throughout the state.

Interesting references for older students about UV
American Medical Association Council on Scientific Affairs. Harmful effects of ultraviolet radiation. Journal of America Medical Association 1989; 262: 380-4.

Blaustein, A.R. et al. Amphibian declines and UV radiation. Bioscience 1995b; 45: 514-515.

Licht, Lawrence E. and Karen P. Grant. The effects of ultraviolet radiation on the biology of amphibians. American Zoology 1997; 37: 137-145.

Click on these links for more information on the possible impacts of UV radiation:

"What's Happening to Our Frogs" (December, 1998)

"Agrichemical, methyl mercury, and UV radiation effects on southern leopard frog (Rana utricularia) and gray treefrog (Hyla chrysoscelis) tadpoles" (March, 1998)

"Effects of methoprene and UV light on survival and development of Rana pipiens" (March, 1998)

"Freaky Frogs, Big Mystery" (1998)

"Frog Deformities Research Not Leaping to Conclusions" (October, 1997)

Are pesticides the problem?

There are many chemicals (called xenobiotics) produced by humans used to fight pests such as fleas and ticks, and one of these pesticides has recently received a lot of attention from scientists studying Minnesota's malformed frogs. Methoprene is a chemical compound that is used to control mosquitos, fleas, and biting flies. In laboratory experiments, water contaminated with methoprene resulted in frog malformities, while control water, without the chemical, did not produce malformities. Some scientists think that methoprene is one of many chemicals that acts like a growth hormone, a protein that may cause amphibians to develop abnormally. However, other people argue that these chemicals have been used for many years, without causing such malformities. Whether methoprene use is a factor in the Minnesota frog problem or not, it is highly likely that there is more than one culprit; in other words, the reason for the frog malformities is probably multivariable.

Interesting references for older students (about pesticides and frogs)
Ouellet, M. et al. Hindlimb deformities (ectromelia, ectrodactyly) in free-living anurans from agricultural habitats. Journal of Wildlife Diseases 1997; 33: 95-104.

Click on these links for more information on the possible impacts of pesticides and fertilizers:

The Herptox Page (Canada)

"Agricultural Runoff May Be Killing Amphibians" (January 5, 2000)

"Induction of Mortality and Malformation in Xenopus laevis Embryos by Water Sources Associated with Field Frog Deformities" (December, 1998)

"What's Happening to Our Frogs" (December, 1998)

"Weird Frogs, Chemicals Linked" (November, 1998)

"Is a new DDT killing frogs?" (Spring/Summer, 1998)

"Freaky Frogs, Big Mystery" (1998)

"Frog Deformities Research Not Leaping to Conclusions" (October, 1997)

What about aquatic toxins?

What is being done?

The Minnesota Pollution Control Agency (MPCA) is actively seeking answers to the problem of the malformed frogs. Several MPCA scientists are busy sampling water and soil, among other things, to determine the cause of these abnormalities. Also, the DNR leads citizen monitoring of frog populations throughout the state:

What about parasites?

Trematode cysts are found to cause damage to developing limb buds, which can result in the growth of extra limbs. While in Minnesota, scientists are concentrating on the two previous areas in their research, scientists in other parts of the country are focusing research on parasites. Click here for more information on the work of one scientist doing research in this area.

"Freaky Frogs, Big Mystery" (1998)

Choose from these other areas:
Amphibian Facts
MN Frogs and Toads
Global Amphibian Declines
MN Frog Watch
Surveying Populations
Malformed Amphibian Photos
Student and School Reports







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