The curious case of missing frogs legs solved
Published on : Monday 29 2009 13:9 - by, ANI
London, June 29 - ANI: A team of scientists has claimed to have solved the curious case of the missing legs in many frogs, by suggesting that the deformed frogs are actually victims of the predatory habits of dragonfly nymphs, which eat the legs of tadpoles.
In the late 1980s and early 1990s, researchers started getting reports of numerous wild frogs or toads being found with extra legs or arms, or with limbs that were partly formed or missing completely. The cause of these deformities soon became a hotly contested issue, with many researchers believing that they are caused by chemical pollution.
But now, according to a report by BBC News, tests on frogs and toads have revealed that the deformities have been caused naturally, by predators or parasites.
The most commonly found deformities are frogs or toads found with missing or truncated limbs, and although parasites occasionally cause limblessness in a frog, these deformities are almost never associated with the trematode species known to cause extra limbs, said Stanley Sessions, an amphibian specialist and professor of biology at Hartwick College, in Oneonta, New York.
The mystery of what causes frogs to have missing or deformed limbs remained unsolved until Sessions teamed up with colleague Brandon Ballengee of the University of Plymouth, UK. As part of this work, Ballengee and Richard Sunter, the official Recorder of Reptiles and Amphibians in Yorkshire, spent time during the summers of 2006 to 2008 surveying the occurrence of deformities in wild amphibians at three ponds in the county.
In all, they found that between 1.2 percent and 9.8 percent of tadpoles or metamorphosed toads at each location had hind limb deformities. Three had missing eyes.
We were very surprised when we found so many metamorphic toads with abnormal limbs, as it was thought to be a North American phenomenon, said Ballengee.
While surveying, Ballengee also discovered a range of natural predators he suspected could be to blame, including stickleback fish, newts, diving beetles, water scorpions and predatory dragonfly nymphs. So, Ballengee and Sessions decide to test how each predator preyed upon the tadpoles, by placing them together in fish tanks in the lab.
None did, except three species of dragonfly nymph.
Crucially though, the nymphs rarely ate the tadpoles whole. More often than not, they would grab the tadpole and chew at a hind limb, often removing it altogether.