Lizard has problem-solving skills

13 July 2011 Last updated at 08:33 By Victoria Gill Science reporter, BBC Nature The lizard used a novel "head-butting" technique to retrieve its treat

A vibrant green tree-dwelling lizard has surprised scientists with its mental prowess by succeeding in a problem-solving test.

The tropical lizard Anolis evermanni was able to associate the colour of a disc with a food reward - flipping over the correct disc to reveal a worm secreted underneath.

The results, published in the Royal Society journal Biology Letters, suggest that reptiles are more intelligent than previously thought.

The scientists gave six lizards the colour discrimination task.

First they concealed a worm underneath a disc to find out if the lizard would be able to negociate the obstacle.

Manual Leal, the Duke University researcher who led the study, explained: "The first thing we wanted to know was: can they flip over the disc to get the worm?"

This humble, well-studied species is known to have a simple foraging method, whereby it scans the horizon for moving prey and strikes it from above.

"But in our experiment," the researchers explained in their paper, "visual cues were absent and striking from above was an ineffective method dislodging the disc."

But the nimble reptiles quickly learned to use one of two methods to dislodge the disc concealing their treat.

They either bit the edge of the disc and dragged it away or, more inventively, ran into the disc, bumping it out of the way with their heads and grabbing the worm.

"I was surprised by this second method," said Professor Leal. "We weren't expecting that level of problem-solving.

"Using their snout as a lever is not simply transferring a natural behavior [to a new task], it's using a new behavior to solve a new problem."

The researchers then presented the lizards with a choice between two differently coloured discs - a blue one and one that was blue and yellow.

"They learned to associate the colour of the disc with a food reward," said Professor Leal.

"And when we swapped the discs around - [so the worm was underneath the other disc] - they were able to reverse what they'd learned."

Colourful life

A. evermanni lives in the canopies of the tropical forests of Puerto Rico, sleeping in the branches or on the tops of leaves. It eats mainly insects.

"They mostly walk or run on the branches, occasionally jumping from branch to branch," explained Professor Leal.

The scientist speculated that colour discrimination might be useful in the lizards' courtship routines.

"Each [Anolis] species has a somewhat distinct colour or pattern," he said. "So rapid discrimination between colours... might be important for females during the mate selection process."

The ability to be flexible might also allow the lizards to explore and adapt to new habitats and search for new food sources.

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