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Tag Archives: Green Frogs

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Chemicals (pesticides, Atrazine, gonadotrophin) and Their Effects on Frog and Fish Sexuality and Reproduction

download (2)Amphibians and fish are highly susceptible to even minute amounts of foreign chemicals in their habitats. As such, their current population declines should serve as an important “early warning signal”, forecasting problems that will eventually affect other animals and ourselves.

An odd twist to this sensitivity issue among frogs is that an injection of gonadotrophin, a human growth hormone, brings many species into breeding condition. This discovery was a boon to captive breeding programs, as most frogs require the duplication of certain environmental cues – dry or wet seasons, for example – if they are to breed normally. However, things can easily go wrong – while using hormones to stimulate breeding, I and others have noted that some male frogs began to develop organs resembling ovaries.

Now, male frogs in the wild are being found to have inter-sex characteristics, including immature eggs within the testes. A recent Harvard University study found such characteristics in 21% of the male green frogs, Rana clamitans, in ponds in suburban Connecticut. It seemed that the affected frogs were more common in suburban than agricultural areas, but other studies have yielded opposite results. Similar reproductive system changes have been documented among catfish in Africa, sturgeon in the Mississippi and other fishes.

Drainage_nitrates_vers_HondeghemFr_2003_04_09Pesticides, the herbicide Atrazine, and other chemicals commonly found in water and soil have been shown to affect sex hormone development, but much more research needs to be done.

There is a great deal of ongoing research in this important area – please read any related articles that you may come across and write in to share new information.

An article describing research into the effects of Atrazine on amphibians is posted at:http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1247376

Amphibian Learning Abilities – the southern toad, Bufo (Anaxyrus) terrestris and bumblebee mimics

While thinking about amphibian learning capacities recently, I was reminded of an experiment recounted in the book Animal Behavior (Time, Inc., 1965), written by Niko Tinbergen, one of the giants in the study of ethology (animal behavior). The experiment was conducted at the famous Archbold Research Station in Florida, in the 1960’s.

The robber fly, which is sting-less and tasty, closely resembles the unpalatable bumblebee. A southern toad, which had previously seen neither fly nor bee, was presented with a robber fly, which was promptly eaten. A bumblebee was then offered – the toad grabbed it, was stung, and spit out the bee. A subsequent bumblebee was refused. Then another robber fly was offered – and, its lesson learned, the toad backed away. To prove that the toad was still hungry, the researchers then provided a dragonfly, which was immediately eaten.

I am not aware of research concerning how long such lessons are retained – but my own experience offers some clues. I have long kept green frogs, Rana (Lithobates) clamitans in an outdoor pen, where I used ripe fruit to attract insects for them to eat. Year after year, I observed the same frogs to studiously avoid yellow-jackets and other wasps, while snapping up flies and beetles located close to the wasps. It would appear that they were stung at one point, and that the lesson lasted, as far as I can tell, for at least 6 years.


The book to which I referred above is one in the wonderful Life Nature Library series published by Time, Inc. Don’t let the publication dates fool you – they are packed with original observations and unique photos.

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