Nancy J. Schmitt
Two prominent biologists/ herpetologists Tyrone Hayes of University of California, Berkeley, and David Skelly of Yale University have been involved in research on frogs. Their research is relevant because much of it has to do with determining the endocrine disruptors' impact on frogs. The research is telling us that even though frogs can evolve quickly to adapt to environmental change, there are concerns as to what is in the water system that is changing the frogs, making their survival less assured.
One contaminant to watch may be atrazine, an herbicide that has been pointed to as the endocrine disruptor that has been feminizing the frogs according to Tyrone Hayes. He suggests that this substance is much more dangerous in smaller amounts than the EPA currently tests for. In fact, he suggests that an amount 30 times less than what the EPA tests for can seriously damage the frogs. Paradoxically, higher levels seem to trigger a defense mechanism in the frogs and do not appear to harm the frogs as much.
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David Skelly isn't so sure that it is the atrazine that is the problem, but suggests that a trematode has a lot to do with frog deformities. Although he has been researching the feminization of male frogs, his primary focus has been the study of extra legs or missing legs. In another apparent paradox, the deformities also happen where the trematodes are not present. Biologist Skelly also observes that he had expected to find a lot of frogs effected around agricultural areas, but that he has found that this isn't so according to his research. It may be a matter of the thresholds of the chemical similar to that observed by Tyrone Hayes in his separate studies in that there may be so much atrazine in the water near farms that the natural defenses of the frogs come into play.
One postulation is that ponds have more fertilizer pollution. Therefore they have more algae, which typically means more snails to eat the algae. The trematodes are parasites of the snails. The trematodes leave the snails and burrow into the tadpoles at the area where their legs are formed. The legs do not form properly and the deformed frogs become easy prey for birds, which eat them and the trematodes. The trematodes lay eggs in the bird which are expelled near the water and the larva find snails to live in. David Skelly has done research in ponds literally in my backyard and has found a disturbing number of deformed frogs.
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Whatever the cause(s), there are issues with frogs throughout the world. This is cause for alarm, because frogs or amphibians have been adapting well to the environment around for 250 million years, yet within the past 30-40 years, it has become evident that they are struggling to survive. Frogs have deformities that have never been seen until recently: too many legs, not enough legs, male frogs having female characteristics, such as male genitalia that develop to become female-like with the possibility of laying eggs, and reduction of male voice boxes, so the call to mate is no longer understood by the female. Currently about 1 in 5-6 or about 18-20% of frogs appear to be feminized.
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