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Questions and Answers '97

Questions and Answers '98

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QUESTIONS AND ANSWERS '96

  1. Do frogs lay different amounts of eggs?
  2. What kind of fish eat frogs?
  3. Why do frogs mainly come out in the rain?
  4. Why are so many frogs killed on the roads?
  5. How small can frogs be?
  6. Why are Minnesota frogs so different from brightly-colored rainforest frogs?
  7. What is causing the deformities in Minnesota's frog populations?
  8. Do the pollutants go up the food chain?
  9. What causes frogs to malform?
  10. How many deformed frogs were in the population first discovered by students at the Minnesota New Country School?
  11. Where do amphibians come from?
  12. Can tree frogs swim?
  13. Can an African frog change to a different sex or a different color? Why or why not?
THE TEAM

Cindy Reinitz
Cindy, a.k.a. "The Frog Lady," is a second grade teacher at Park Elementary School in Le Sueur, Minnesota. During the 1995-96 school year she took a leave of absence to teach at the Minnesota New Country School, a charter school in Le Sueur. It was while teaching here that Cindy's students discovered the deformed frogs that were the impetus for A Thousand Friends of Frogs. In addition to her teaching, she is helping develop the Ney Environmental Learning Center near Henderson, Minnesota.

John Moriarty
John Moriarty has extensive expertise in matters herpetological. His experience includes work as a wildlife specialist for Hennepin Parks in Minnesota and participation in surveys of frog populations in southwestern and southeastern Minnesota. He is the co-author of Amphibians and Reptiles Native to Minnesota and currently serves as the Co-Director of the Minnesota Frog and Toad Survey.

Judy Helgen
Judy is a research scientist with the Minnesota Pollution Control Agency (MPCA). When she learned of the discovery of deformed frogs by Cindy's students, she thought that thousands of youth could help look after the health of our amphibian friends.

Sehoya Harris
Sehoya is a conservation biologist who has studied frogs as well as coyotes and red wolves. For her frog studies she has spent three years in the rain forests of Ecuador in South America. This experience was part of her work toward a Ph.D. degree at the University of Minnesota.

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QUESTIONS & ANSWERS '96
  1. Do frogs lay different amounts of eggs?
    (Submitted by the O.H. Andeson School, Mahtomedi, MN)

    • Moriarty: Yes. Frogs and toads can lay from two to over 20,000 eggs at a time. In Minnesota, the number of eggs varies from 200 (Western Chorus Frog) to 20,000 (Bullfrog) eggs per year. Frogs lay their eggs in small clumps, long strings, floating masses, or large surface films.
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  2. What kind of fish eat frogs?
    (Submitted by the O.H. Anderson School, Mahtomedi, MN)

    • Moriarty: Most predatory fish, from a stickleback to a muskie, will eat frogs. Smaller fish will normally prey on eggs, while larger fish prey on tadpoles and adults. Northern Leopard Frogs are commonly sold as bait for bass and northern pike fishing. Most frogs pick lakes and wetlands that are absent of fish for breeding ponds. This way, frog eggs and tadpoles will not be eaten. When humans add fish to a pond or wetland it can lead to the elimination of amphibians from that area.
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  3. Why do frogs mainly come out in the rain?
    (Submitted by the Clayton Public Schools)

    • Moriarty: Frogs come out in the rain because they do not have to worry about drying out. An amphibian's skin is permeable to water and if the humidity is too low they will lose water and start to dry out. This is very stressful to the frogs. Frogs have adapted to water loss by developing less permeable skin, as in toads, or seek micro-habitats with higher humidity.
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  4. Why are so many frogs killed on the roads?
    (Submitted by the Clayton Public Schools)

    • Moriarty: Humans have built too many roads! Roads fragment the habitats that frogs use for breeding, feeding, and hibernating. When frogs migrate from one area to another they normally have to cross a road. A frog's defense when a car drives by is to crouch down. When that happens they become "sitting ducks." In Europe people are building frog corssings or tunnels to allow frogs and toads to safely get across roads.
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  5. How small can frogs be?
    (Submitted by Elizabeth Winters' class, Rochester, MN)

    • Moriarty: As adults, the smallest frogs are the narrow-mouth toads of Africa at 1 cm. (less than 1/2 inch). In Minnesota the smallest frog is the Spring Peeper at 2-3 cm. (about 1 inch). A newly transformed Spring Peeper can sit on a dime and not have any part of its body sticking over the edge.
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  6. Why are Minnesota frogs so different from brightly-colored rainforest frogs?

    • Harris: That is a very good question. Actually, scientists are not sure why they are so different, and there are many different ideas for why we don't have really colorful frogs here in Minnesota. You may already know that the bright red and blue frogs in the rainforest are poisonous, and their colors are used to warn other animals to leave them alone. Some scientists think that most of the animals in Minnesota that like to eat frogs are actually color-blind. That is, they can't tell if a frog is yellow or gray, so why should a frog bother being so colorful? Our frogs are usually the color of the ground (okay, maybe that isn't so exciting) so that frog-eaters can't see them very well. Some biologists think that the tropics have had more time to allow more types of animals to develop because they were not covered by huge glaciers ten thousand years ago. Minnesota WAS covered by glaciers during this time, and so there were no frogs here then. Also, many people don't know this, but there
      are actually A LOT of really drab frogs in the tropics as well. Obviously something is going on, though, because we see the same pattern with birds. Many of the birds in the rainforest are much more colorful than our birds. We may never completely answer this question, so maybe you should consider studying this topic in college.
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  7. What is causing the deformities in Minnesota's frog populations?

    • Helgen: No one is sure yet. But MPCA staff and other researchers are testing the mud, water, and frog tissues for abnormal levels of metals such as arsenic, mercury, selenium and cadmium. They're also looking for chemicals like PCBs, herbicides and pesticides, and also at parasites as potential causes. There are many theories. But so far, there's no evidence pointing to any one possible cause over another. Researchers speculate the deformities may be the result of genetic mutations passed on from the parent frogs to their offspring. There is no evidence at this point to suggest that human health is being endangered by whatever is causing the deformities.
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  8. Do the pollutants go up the food chain?

    • Helgen: Many of the pollutants we are considering as possible causes and analysing do "bioaccumulate" and move up the food chain. This is especially true of some of the heavy metals like mercury. Many of the organic compounds we are considering such as many of the herbicides can bioaccumulate especially in the fatty tissues of frogs and other animals.
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  9. What causes frogs to malform?

    • Helgen: This is the question everyone wants to know the answer to. Right now we don't know. We have some ideas we are considering and we're doing tests to find out how likely they are to be the cause. These inlcude:
      1. Increases in the ultraviolet radiation due to thinning of the ozone,
      2. Heavy metals which are know to cause abnormal development, particularily; Selenium, Arsenic, cadmium, and Mercury,
      3. Organic compounds like PCBs (Poly-chlorinated biphenyls) and Biocides (Herbicides and pesticides),
      4. Parasitic cysts physically disturbing the developing limb bud in tadpoles and,
      5. Synthetic chemicals that act like hormones to disrupt the endrocrine system.
      We probably won't know the answer until after several years of tests.
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  10. How many deformed frogs were in the population first discovered by students at the Minnesota New Country School?

    • Reinitz: On the day the frogs were first discovered, the students from the Minnesota New Country School looked at 22 frogs, half of which were deformed. Within a month they had collected roughly 400 deformed frogs from the Ney Pond. Most of those frogs were turned over to researchers for study.
      (For the full story, jump to the Minnesota New Country School website: http://www.mncs.k12.mn.us/frog/frog.html.)
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  11. Where do amphibians come from?

    • David Hoppe: Amphibians are thought to have evolved from a group of extinct fishes known as the rhipidistians. Those fishes had fleshy, muscular fins to move along the bottom and push themselves through thick vegetation in shallow waters--fins that are logical forerunners to amphibian legs. They also had a tube connecting from the gut to the swim bladder, so they could swallow air and have some get to the swim bladder as a way to receive some oxygen. Thus, the swim bladder served as a primitive lung, useful to the fishes in warm, shallow waters that had little oxygen, and became logical forerunners to the amphibian lung. Return to top of page

  12. Can tree frogs swim?
    (Submitted by Brianna in Rochester)

    • Harris: Yes, tree frogs are able to swim, and swimming is actually a very important part of their lives. Many tree frogs lay their eggs on the underside of leaves, and when the tadpoles hatch, they fall into a body of water that--hopefully!!--is directly beneath the leaf. As you can probably imagine, these tadpoles must be able to swim immediately. When they develop into adult frogs, they will climb into the trees and spend the rest of their lives away from the water, until it is time to lay eggs of their own.
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  13. Can an African frog change to a different sex or a different color? Why or why not?
    (Submitted by Kelly and Shannon in Rochester)

    • Harris: From your question, it seems that you have learned that certain frogs change sex and many frogs change color on a regular basis. Unfortunately, there are so many types of frogs in the world, and I can't say for sure if there are specific frogs in Africa that change sex. My guess is that there are frogs like this in tropical Africa, because sex change in frogs is not uncommon around the equator. These changes seem to have something to do with temperature changes around the tadpole eggs but scientists aren't sure why this would be useful to frogs. I AM sure that African frogs do change color, because this behavior is typical of frogs everywhere, including Minnesota. Sometimes they change in response to time of day, other times they change because of their level of activity. I have seen a frog in South America change from white to yellow to orange in just a few minutes, and I think the changes were due to the frog waking up.


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