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.
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 Duke University and the results, published in the Royal Society journal Biology Letters, suggest that the problem-solving abilities of reptiles may be greater than previously thought.
The Puerto Rican lizard, (an anole), used in the study, is a well-studied species, known to excel at foraging food by being acutely aware of movement.
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 learned to associate the color of the cap with a food reward," said Manual Leal, the Duke University researcher who led the study.
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.
And when the color of the caps was switched, after a few mistakes two of the lizards were able to figure out the trick.
Jonathan Losos, a biologist at Harvard University 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.