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Discovery.com News
  May 15, 2001 SEARCH  

The Secret's in the Suction

Meet Bizarre Lizards

Chameleon Tongue Tells Tale

By Oliver Baker,
Discovery.com News

Oct. 17, 2000 — The secret behind the sticky thwop of a chameleon's tongue as it sticks and grips its prey is finally out: the tongue fastens itself to victims with suction, an international team of biologists says.

Squeezing a slippery knob in the throat, a chameleon tongue launches itself at targets up to two body lengths away, then retracts with its quarry like an accordion.

But Belgian biologist Anthony Herrel says it was not these ballistics that startled him. After having studied how other lizards feed for eight years, he saw a chameleon lasso a lizard nearly the same size as itself.

"They're not supposed to do that," says Herrel.

The tongues aren't big enough or sticky enough to bag such big game with simple adhesion, he says.

An idea raised in 1983 by evolutionary biologist Kurt Schwenk suggested an explanation. Schwenk had described the muscles beneath the tip of a chameleon's tongue, which forms a flat pad at rest, but in flight, dimples into a deep, conical mitt that engulfs the target.

With these muscles the mitt might act like a suction cup, Schwenk hypothesized, and achieve a seal with the tongue's moistness.

In the current issue of the Journal of Experimental Biology, Herrel and colleagues describe testing the idea by shaping the flaccid tongue pouches of anaesthetized chameleons around a straw that was either sealed or open at both ends. They then electrically stimulated the muscles to contract.

Around the sealed straw the pouch was airtight, but the open straw allowed air to enter. With a tug on the straw, the researchers assessed the tongues' grip. They clung with two-and-a-half times the force to the sealed straw.

"It's a beautiful paper," says Schwenk, who now teaches at the University of Connecticut in Storrs.

Additional tests included recording muscle contractions from dangling wires in awake chameleons as their tongues hurled through the air, as well as X-ray and high-speed movies. Herrel and colleagues put ten species of chameleons from Africa and Madagascar through the tests, and conclude they're all doing the same thing.

Herrel says chameleons' iron grips support their sedentary lifestyle. It means they can bag pretty much whatever walks or flies in range.

"That's pretty important if you're not going to move much," he says.

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Picture: Courtesy of Anthony Herrel et al. |
Copyright © 2000 Discovery.Com & Oliver Baker


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