In the United States in the early 1990’s

Specifically the state of Minnesota

A troop of boy scouts.

Were learning about aquatic ecosystems…and catching frogs.

Traditionally you would expect that the boys would have found frogs like these…but they didn’t. Rather they found frogs like…

this… and this!

• The troop recognizing a major problem and scared for there community, informed the authorities.

• The authorities then informed the United States Environmental Protection Agency (EPA) who worked with a number of other researchers to determine the cause.

• First the researchers had to do some base line research

Communities History:

• First the scientists went back to records from the 50 – 60’s to determine if these abnormalities had been witnessed previously in this area.

• The researchers apparently found some information from 1950’s

• A sample of a hundred frogs from the same community would have had on average 5 abnormal frogs.

• Of these frogs, on average only 1 would have had multiple legs

• The current sample had on average 80 out of a 100 frogs with deformities. More than 50% of these abnormal frogs had multiple legs.

Right away the scientists created experiments to test the hypothesis that these abnormalities were being caused by increased UV or pesticide/industrial waste exposure.

The EPA tested the effects of…

1. Full spectrum florescent light exposure (normal light)

2. Ultra violet light exposure

(UV light)

On tadpoles!

All normal!

Many abnormal …but NO multiple legs

The EPA tested the effects of a number of commercial and agricultural pesticides on tadpole development. (The exact chemicals I am unsure of)

The pesticides the EPA tested did not induce major teratogenic effects. Most of the frogs were normal.

1) Unclear about what is going on, the EPA needed to do more research.

2) They went back to the community in question and conducted a variety of sampling techniques.

3) They realized that there was an abnormally large snail population.

Snails can be a primary host for a parasite called a fluke. (not actual trematode in question)

2) So the EPA tested trematode exposure on a tadpole population

1) Trematode or Fluke (not actual trematode in question)

3) The flukes embedded themselves in the cloaca (leg) region of the tadpole.

4) Frogs with multiple leg deformities developed.

The million dollar question here being….

Why does the Trematode or Fluke only inbed itself in the cloaca region of the frog!

THINK FOOD CHAIN!

Figure it out before the next slide…combine your knowledge of life cycles, parasites and food chains to get the answer.

•The flukes final and most important host is a large predatory bird like a heron or egret.

•By causing teratogenesis of its legs it prevents the frog from escaping these formidable predators.