When the weather cools, ectothermic (cold-blooded) animals slow down, which should be good news for their potential prey. But the colorful chameleon has found a way to keep feeding at top speeds even in lower temps: an elastic-tissue tongue, which unlike regular muscles, can uncoil nearly as fast in lower temperatures as it can in warmer ones.
The chameleons' weapon is fast, rolling out as far as twice the lizard's body length as quickly as 0.07 seconds (some species' tongues accelerate from zero to six meters per second in just 20 milliseconds, according to a 2004 study). Triggered by a muscle, the collagen tissue tongue then uncoils based on momentum, and this direct flow of kinetic energy travels more rapidly than it could through muscle, noted researchers Christopher Anderson and Stephen Deban, both of the Department of Integrative Biology at the University of South Florida in Tampa.
"This feeding mechanism is common to all chameleons and gives these slow, cryptic, sit-and-wait predators the element of surprise," Anderson and Deban wrote in their report, published online March 8 in Proceedings of the National Academy of Sciences.
As ectotherms, lizards—including the clever chameleon—depend on the external temperature for their overall body temperatures (and in turn their muscle function). A drop of 10 degrees Celsius means a decrease of about 33 percent in speed and a similar flagging of strength for most cold-blooded creatures, according to the researchers.
They found that other ectothermic animals' muscle-based tongue movement slowed to about half-speed (42 percent) if temperatures dropped 10 degrees Celsius. But veiled chameleons (Chamaeleo calyptratus) tested by researchers (by tempting the lizards with crickets dangling from a thread) had tongue snaps that only slowed by about 10 to 19 percent and did not become shorter with the same temperature decrease.
"Chameleons feed over a wider range of [body temperatures] than other lizards," Anderson and Deban wrote. There are more than 100 different chameleon species on Earth, some of which inhabit locations where temperatures climb above 39 degrees Celsius or dip below freezing. Whereas the hotter weather would seem ideal for many ectotherms, the researchers noted, scientists had been unsure how the lizards could capture prey at low temperatures. The new findings explain how the lizards are able to maintain such an extensive feeding niche.
The lizards, however, weren't quite as quick to reel their prey back in as temperatures cooled. Although uncoiling depended on the quick snap of elastic tissue, the recoiling action depends on muscle contraction. And with the 10 degrees drop, the recoiling performance fell by 42 to 63 percent, the authors reported.
Chameleons aren't the only creatures to take advantage of the quick elastic tissue trick, the researchers pointed out. It has also been found in the projecting tongues of salamanders and the striking action of mantis shrimp. Now, the new discovery of the relative temperature independence of this movement presents a way for researchers to search for it in other species.
Images of veiled chameleons courtesy of Christopher Anderson