Lizards are capable of problem-solving, study shows

July 15, 2011

A tropical tree-dwelling lizard has succeeded  in a problem-solving test by learning to associate the color of a cap with a food reward, contesting the stereotype that reptiles are extremely limited cognitively compared to birds and mammals. The cognitive abilities of reptiles have rarely been studied.

In a color discriminating task, the lizards learned to flip over the correctly colored cap to reveal a worm hidden underneath. The experiment was conducted at and the results, published in the, suggest that the problem-solving abilities of reptiles may be greater than previously thought.

The Puerto Rican lizard, (an ), used in the study, is a well-studied species, known to excel at foraging food  by being acutely aware of movement. Several lizards of this species were collected from Puerto Rico for the experiment.

Researches first wanted to determine if the six lizards used in the study were able to figure out how to flip off the cap to obtain the food. The agile reptiles quickly learned to use one of two ways to move the cap: they closed their jaws on the edge of the cap and dragged it off the food, or ran into the cap with their heads, tipping it over and grabbing the food. The lizards were then given a choice between two caps; one was blue and the other was yellow and blue; under only one was the food reward of a worm. They quickly learned to distinguish which cap had the reward.

"They learned to associate the color of the [cap] with a food reward," said Manual Leal, the Duke University researcher who led the study. Their success on a test that is based on worms and usually used on birds was "completely unexpected," he said.

The lizards solved the problem in fewer tries than birds needed to flip the correct cap and pass the test, Leal explained. Lizards get just one chance per day because they eat less, while birds usually get up to six chances a day. Thus a mistake by a lizard means it must remember until the next day how to correct the mistake, Leal said.

And when the color of the caps was switched, after a few mistakes two of the lizards were able to figure out the trick. "We named these two Plato and Socrates," said Leal.

Jonathan Losos, a biologist at not involved in the study, said Leal's experiment demonstrates that when faced with a new situation, most of the lizards were able to solve the problem. They had the ability to figure out the trick and disregard their previous learning; a sign of a cognitively advanced animal that some mammalian species cannot easily do.

The results "should cause researchers to re-evaluate what they think they know about the evolution of animal cognition," Losos said.