limblessfrogsThe mystery of the deformed frogs is a news story that pops up every now and then on the evening news or PBS “" supposedly, we like to be reminded every few months about how each of us is personally responsible for slowly but surely ruining the entire planet. Up until this point, scientists had proposed that the chemicals we were leeching into the environment and therefore into the frogs’ watery homes was interfering with their development, causing frogs to be born without limbs, with extra limbs, or other abnormalities.

While in pictures these malformed frogs were obviously eye catching for the environmentalist crowd, it turns out there’s actually a much more benign and biological explanation beyond all the fear mongering. The missing limbs and the extra limbs actually have two completely separate causes. While some scientists are still firmly entrenched in the “chemical cause” camp, biologists Stanley Sessions and Brandon Ballengee observed tadpoles in the wild for a few years, and noted that the tadpoles were actually being predated on by dragon fly nymphs.

The scientists observed back in their lab that the dragon fly nymphs would, more often than not, eat only parts of the tadpoles, usually just removing a limb. The tadpoles would then return back, and grow up, sans said limb. Despite missing parts of their bodies, many of the tadpoles were still able to grow up, metamorphosizing into frogs, who managed to live quite a long time.

While frogs with missing limbs have a rather mundane explanation, the frogs with extra limbs have a much more exotic explanation. Sessions established that the frogs had been infested by small parasitic flatworms called Riberoria trematodes. These works burrowed into the rapidly developing tadpoles and actually rearranged the cellular structure of the frogs as they were developing, resulting in their leg precursor cells to actually spawn multiple limbs.

Of course, the fact that this problem turned out not to be our fault doesn’t mean we’re off the hook. Pollution is still a problem, even if its effects aren’t as obvious as a three-legged frog.

About The Author

Michael Kaufmann, lover of all things science and gadget, is a contributing editor at Blast. He can be reached at [email protected].

2 Responses

  1. Kevin

    Sigh. We are so quick to grasp at any opportunity to ‘absolve’ ourselves of responsibility and scoff at those ‘fear mongering environmentalists.’ It’s the option that allows us to continue with our bad behaviors and feel the least amount of responsibility and guilt for our actions. But anyone who takes an in-depth consideration of this topic will see that there is so much more involved than just fish nibbling on tadpoles, and that perhaps “each of us is [indeed] personally responsible for slowly but surely ruining the entire planet.” Can, as Sessions et al. suggest, fish predation cause missing limbs? Of course. No one ever said that wasn’t one of the causes. But it is not the explanation for all or even most missing limbs or, as the blogger rightly points out, multiple limbs. Most missing limbs and deformations are the cause of a natural parasite, as again the blogger rightly states. However, that parasite (and resultant deformities) is made unnaturally more abundant by human activities, including the pollution of wetlands and waterways with fertilizer that causes blooms in algae and booms in snail populations, including snails that act as a host for the deformity-inducing parasite. Read for yourself The blogger (and anyone interested in the truth) would do well to read this comprehensive book on the subject There is no doubt that humans are behind the majority of amphibian deformations. We are also the cause of the modern day amphibian extinction crisis. Did you know we are on the verge of losing between one third and one half of this group of animals, a group that has been around so long they watched the dinosaurs come and go? Amphibians are a fundamental component of healthy ecosystems, sensitive indicators of environmental health, and vital contributors to human health. We would do well to take a little responsibility for these animals, for all living things, including ourselves. There is no alternative to a healthy planet.

  2. Mike

    The study by Ballengee and Sessions puts forward an interesting potential explanation for some types of frog deformities. Unfortunately, their research fails to live up to the media hype; it does not solve the mystery of deformed frogs. In the laboratory, they found that some dragonfly larvae will remove limbs of tadpoles. However, Ballengee and Sessions did not actually test the predictions of the dragonfly hypothesis with rigorous data from the field. For example, a clear prediction of their hypothesis is that as the frequency of dragonfly larvae in wetlands increases, the frequency of missing-limb deformities in those wetlands is also expected to increase. Ballengee and Sessions did not test this prediction. Testing such predictions is a fundamental component of science. Until there are well-designed studies that examine the relationship between dragonfly density and frogs with missing limbs in nature, the relative importance of the role of predation in amphibian deformities will remain unknown.


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