Chilled Chameleons Still Quick to Snag a Meal (LiveScience.com)

Chameleons' high-speed tongues can still shoot out lickety-split

to capture prey in cold temperatures, when their other muscles don't move as

fast, a new study finds.

As a result, the reptiles can keep chowing

down across a range of temperatures, regardless of how fast the rest of their

bodies move.

Since these cold-blooded creatures, or ectotherms, rely on

heat from the surrounding environment to warm their bodies, their muscles can't

function as well when it's chilly outside.

Why doesn't the tongue also succumb to the cold? It's

powered by a special mechanism, one that separates the tongue's

projectile-like motion from direct muscle contraction, and allows it to

accelerate at 41 Gs, said Christopher Anderson, a researcher at the University

of South Florida. One G is the normal force of gravity. An astronaut feels about 3.5 Gs during a space shuttle liftoff.

A mere 8 Gs will cause most people to black out.

Until now, scientists thought the main advantage of this

tongue mechanism over muscle contraction was just for speed. But the new study

shows it has cold-weather benefits as well, Anderson said.

And humans could perhaps use a similar design for devices

that need to maintain their performance in low temperatures, such as prosthetic

limbs and sports equipment, he said.

Ballistic tongues

Colder temperatures can have a considerable impact on

lizards and other ectotherms, affecting their ability to gather food and flee

predators. In fact, a 10-degree drop has been shown to reduce speeds in lizards

and fish, and jumping distances in frogs by at least one-third, the researchers

say.

But chameleons maintain their ability to feed across the range

of temperatures in their habitat, from 38.3 degrees Fahrenheit (3.5 degrees

Celsius) in mountain areas to above 100 degrees F (39 degrees C) in the desert.

Chameleons owe this ability to their unique tongues, which

are launched via a stretch-and-release mechanism, similar to that of a bow and arrow.

First, a muscle gradually contracts and stretches elastic tissue in the tongue,

which stores up energy. Then, at the right moment, this energy is released,

allowing the tongue to reach the prey in about 70 milliseconds, or about five

times faster than the average eye-blink.

At lower

temperatures, the muscle contracts more slowly, but this doesn't affect how

much energy is stored in the elastic tongue tissue.

"It's like shooting a bow and arrow," Anderson

said. "It doesn't matter how slowly you pull the bow back...the same amount

of energy is going to be released."

Bringing the tongue back into the mouth does require direct

muscle movement. These two different mechanisms allowed the researchers to test

whether the stretch-and-release system really is more resistant to the cold

than muscle-powered movements.

Cold-proof

They compared the performance of tongue projection versus

retraction at 59 degrees F (15 degrees C), 77 degrees F (25 degrees C) and 95 F

(35 degrees C).

A 10-degree-Celsius drop caused more than a 42 percent decrease

in the tongue's retraction speed. But the same temperature decrease caused only

a 10 percent to 19 percent drop in the speed and power of the tongue's

projection.

Other animals, such as frogs

and salamanders, might also use this elastic mechanism, because of its

ability to withstand low temperatures, Anderson said.

The results were published this week in the journal

Proceedings of the National Academy of Sciences.

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