Chameleons have weatherproof tongues

Image: Chameleon tongue
Chameleons, such as this one, feed by way of ballistic tongue projection, which achieves remarkable performance due to elastic recoil.
/ Source: Discovery Channel

Cold conditions normally slow down muscle performance, helping to explain why Winter Olympics athletes and others warm up before physical activity.

Chameleons, however, could easily win a gold medal for tongue projectile speed. New research has found that the tongue of this lizard shoots out like a rubber band gun, maintaining high function at even very low temperatures.

Understanding how chameleons' ballistic tongues work could lead to advancements in prostheses, sports equipment and more.

The chameleon's near weatherproof tongue gives these reptiles an edge over competitors. These lizards can exploit a wide range of environments as well as early morning peaks in prey activity even in the chilliest of alpine climates, according to the new study, published in this week's Proceedings of the National Academy of Sciences.

Lead author Christopher Anderson, a University of South Florida integrative biologist, told Discovery News that a chameleon's tongue works similar to a spring in a ballpoint pen, a rubber band handgun or a bow and arrow.

In each case, he said, "a temperature-dependent muscle, or muscles, must initiate the mechanism," creating kinetic energy that then decouples from that first movement. This allows the spring, rubber band, arrow or tongue to shoot out "on its momentum alone once launched."

"A chameleon's tongue travels at accelerations exceeding 400 meters (1,312 feet) per second squared, or about 41 Gs of force," he added. To put that into perspective, a space shuttle only develops about three Gs of force when it takes off.

For the study, Anderson and co-author Stephen Deban filmed five veiled chameleons (Chamaeleo calyptratus) feeding on crickets at a range of distances. They placed the insects on what they called a "cricket trapeze," so that the chameleon's tongue could complete its trajectory naturally without being stopped by an immovable target. In the wild, chameleons eat everything from birds and other lizards to all sorts of bugs.

The researchers next lowered temperature during the feeding events. Prior studies determined that when other animals sprint, swim and jump, their muscle power decreases by at least 33 percent over each 10-degree Celsius (18-degree Fahrenheit) temperature drop. Chameleon tongue speed, in contrast, fell by only about 10 percent over this same temperature reduction.

"Since chameleons worldwide feed in a similar manner, we believe our findings apply to all chameleons, from species living in desert habitats to those in alpine zones," Anderson said.

He explained that contraction of the chameleon's tongue accelerator muscle, which is wrapped in circular fashion around the rigid tongue bone, leads to "rapid elastic recoil of collagen tissue within the tongue." About the only thing that might stop this nearly 8-inch-long recoil is extremely hot weather that can break down the tissue, essentially cooking the tongue out of operation.

Normally, however, the tongue shoots out in less than the blink of an eye. Prey then adheres to the tongue due to, in part, a suction vacuum effect and a sticky mucus layer on the tongue that acts like super glue. The tongue rolls back into the mouth, carrying the stunned victim with it.

The researchers suspect that toads and salamanders have equally near weatherproof ballistic tongues.

In the future, the scientists hope that studies on all of these ballistic tongued animals may lead to advancements in prosthetic devices, sports equipment and other objects that often operate using elastic recoil mechanisms. Anderson explained that even walking humans, without device assistance, rely on elastic recoil to improve step efficiency, but the effect clearly isn't as dramatic as a chameleon's speedy tongue.