Salamander's elastic tongue powered by 'coiled spring'

Salamanders' tongues release at very high speed no matter the temperature, but the cold does slow their tongues' retraction

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Salamanders can snatch up prey in a few thousandths of a second - striking out with elastic tongues.

Scientists have now found that the amphibians, which depend on the ambient temperature to heat their muscles, maintain this strike speed in the cold.

But, as footage of the animals has revealed, low temperatures do slow the retraction of their deadly tongues.

The findings are reported in the Journal of Experimental Zoology.

Dr Stephen Deban from the University of South Florida had already studied this effect in other amphibians and reptiles.

"We previously found that tongue projection in toads and chameleons is independent - or nearly so - of temperature," Dr Deban told BBC Nature.

Start Quote

The tongue is launched by the elastic recoil”

End Quote Dr Stephen Deban University of South Florida

"We then turned to some older films we had of salamanders."

He and his colleague, Jason Richardson, focused on Hydromantes platycephalus, a salamander species that can shoot its tongue a distance of 80% of its body length in less than 20 thousandths of a second.

They filmed super slow-motion footage of the animals as they struck out at fly larvae on a platform in front of them.

The scientists wanted to know if, like in toads and chameleons, the muscles that powered the tongue's projection acted like a coiling spring - storing up energy then suddenly letting go and releasing the tongue at extremely high speed.

They studied the animals as they snatched up the larvae over a ranged of temperatures - from 2C to 24C. The salamanders projected their tongues just as quickly and just as far over the whole of this temperature range.

'Cold-blooded sniper'

Dr Deban likened the animals' tongue to an arrow being shot from a bow.

"In the salamanders, and toads and chameleons, the tongue is launched by the elastic recoil," Dr Deban said.

"When they're cold, they can still 'pull back the bow', but it takes longer. However this doesn't matter because the recoil still launches the tongue quickly."

But the muscle-powered process of retracting the tongue was significantly slower at lower temperatures.

The researchers described the salamanders as "cold-blooded snipers". Despite depending on the external temperature to warm their muscles, the amphibians are still able to outmanoeuvre their prey in the cold; elastic recoil seems to be the evolutionary trick allowing them to do this.

The scientists were keen to clarify the term "cold-blooded", which - although a familiar description used for many reptiles, amphibians and fish - can be misleading.

"Cold-blooded animals, like lizards, can actually reach very high body temperatures," Dr Deban explained. This is particularly true of desert-dwelling reptiles.

Animals whose body temperature is determined by their environment are known, in scientific terms, as ectothermic or poikilothermic.

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