05 July 2009

Three-legged amphibians - explained


Amphibians are considered to be highly sensitive markers of water quality, and thus of environmental dangers. About 20 years ago there was concern that the discovery of frogs and toads with absent or deformed legs was a result of an unknown environmental toxin. Now an explanation has been offered:

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.

"Often the tadpole is released and is able to swim away to live for another day," says Sessions. "If it survives it metamorphoses into a toad with missing or deformed hind limbs, depending on the developmental stage of the tadpole."

If tadpoles are attacked when they are very young, they can often regenerate their leg completely, but this ability diminishes as they grow older...

Adult amphibians with one one hind limb appear able to live for quite a long time, Sessions says, explaining why so many deformed frogs and toads are discovered...

And the reason they eat only the hindlegs:

As toad tadpoles mature, they develop poison glands in their skin much earlier than those in their hind legs, which could make the hind legs a far more palatable meal.

Via Neatorama and its Upcoming Queue.

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