Ballistic chameleon tongue beats the cold

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The chameleon's lightening fast tongue is literally one of nature's most striking adaptations.

However, the elastic mechanism that powers the tongue has only relatively recently been fully explained.

Now new research has revealed that the chameleon's spring-loaded tongue can also beat the cold and work at low temperatures.

This makes the cold-blooded lizard an effective hunter even in cooler temperatures, say scientists.

The discovery will also help scientists understand how temperature may effect other species, such as frogs and humans, that use elastic elements such as tendons and muscles, to store and release energy when moving.

The researchers publish their findings in the journal Proceedings of the National Academy of Sciences.

Cool lizard

At low temperatures most lizards and other animals that control body temperature from external sources, known as ectotherms, are unable to move that well.

Our study could help understand how temperature would effect a wide range of behaviours in other animals
Christopher Anderson
University of South Florida, US

"Early in the morning or on cold days, lizards and other ectotherms tend to be inactive and have to bask to elevate their body temperature," says Mr Christopher Anderson from the University of South Florida, Tampa, US who undertook the study along with Dr Stephen Deban also from the University of South Florida.

"The result is that most lizards, which have to chase down their prey, are unable to forage effectively at low temperature," says Mr Anderson.

Rather than chase down their prey, chameleons use stealth, ambushing insects using a super ballistic tongue that extends up to two body lengths away.

Scientists only fully explained how this worked in 2004, discovering that chameleons rapidly project their tongue using a spring-loaded mechanism that stores energy, like a compressed telescope.

When the chameleon strikes, the elastic energy is released in just 20 milliseconds.

Super sharp shooter

"It remained to be explained, however, how an explosively dynamic movement that relies on elastic recoil such as ballistic tongue projection in chameleons is effected by temperature," Mr Anderson explains.

Reports had suggested that wild chameleons may be active earlier in the day and at lower body temperatures than other lizard species that live in the same habitat.

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Using a high speed camera called a photron, which is also used by film makers, the researchers videoed chameleons feeding in hot and cold temperatures.

"We filmed veiled chameleons Chamaeleo calyptratus feeding at 15, 25 and 35 degrees C," Mr Anderson says.

The team found that the chameleon's tongue was able to efficiently shoot out over a wide range of temperatures.

For example, if the temperature dropped by 10 degrees C than the tongue's performance, measured as peak velocity and power, declined between 10% and 19%.

However, the chameleon is less good at retracting its tongue in the cold, with performance dropping by 42% with a 10 degrees C temperature drop.

That is probably because the lizard uses normal, non-elastic muscles to withdraw its tongue after a strike.

Elastic advantage

Because elastic recoil mechanisms appear to perform significantly better at lower temperature than normal muscles, animals that use them may be an advantage in the cold, Mr Anderson says.

Kangaroos, jumping bushbabies, springtail insects and the mantis shrimp all use different forms of elastic tissue to move, for example.

"Our study could help understand how temperature would effect a wide range of behaviours in other animals," Mr Anderson says.

"Even walking in humans incorporates elastic elements that act as springs."

"The principle of elastic elements exhibiting relative thermal insensitivity, as seen naturally in chameleon feeding, could possibly be applied to prosthetic devices or sports equipment."

Mr Anderson and colleagues hope to continue researching other animals that use ballistic tongues to feed, such as toads and salamanders.