Chameleon tongues snappy even when cold

Elastic collagen tissue provides an edge over other cold-blooded hunters

Cool weather typically weakens muscle power in cold-blooded creatures, but new data show that chameleons can nab prey even at near-freezing temperatures thanks to an elastic, energy-storing sheath of collagen inside their tongues.

QUICK TRICK A chameleon doesn’t depend on muscle power to flick its tongue, so it can nab prey in cool temperatures that stymie other cold-blooded predators. C.V. Anderson

Although most chameleons live in warm climates, some live in alpine ecosystems and can feed when their body temperatures are as low as 3.5° Celsius — a trick that scientists haven’t been able to explain, says Christopher V. Anderson, a biologist at the University of South Florida in Tampa.

Now, data suggest that the chameleon’s trick lies in a clump of rubbery tissue at the base of its tongue. Using elastic collagen instead of muscle power to shoot its tongue at prey lets chameleons catch breakfast even when their muscles are stiff from the cold, Anderson and University of South Florida colleague Stephen M. Deban contend online March 8 in Proceedings of the National Academy of Sciences.

At a temperature of 35° C, the veiled chameleon Chamaeleo calyptratus can flick its tongue toward prey at an average of 4.4 meters per second, the team’s tests show. That amounts to an acceleration 44 times Earth’s gravity, or almost five times that of a fighter jet in a high-speed turn. Drop the temp to a chillier 15° C, and the chameleon’s tongue-shooting speed falls to about 3.4 m/s.

That’s a decline of about 23 percent. But the speed at which the chameleon pulls its tongue back in falls off by around 58 percent over the same temperature range.

The dramatic difference, Anderson and Deban contend, is that a chameleon’s tongue retraction is powered by muscles, which are slow to contract in cool temperatures. The tongue-extending action, however, is driven by energy stored in a rubber band–like collagen sheath that surrounds the bone in the base of the tongue. That biophysical modification, a trait common to all chameleons, lets the creatures forage in conditions too cool for other lizards in the same ecosystem, the researchers note.

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