Puerto Rican anoles, Anolis evermanni, were tested on a food-finding apparatus normally used on birds. The lizards showed they could solve a novel problem, remember solutions and 'unlearn' incorrect approaches.
Credit: Manuel Leal, Duke University
BUCKINGHAMSHIRE: Tropical lizards are much better at problem solving and remembering associations than biologists had previously considered, a new study has shown.
The simple experiment, originally devised for birds, tested the Puerto Rican anole lizard's cognitive ability in a series of tasks and discovered that they were adept at both learning and remembering associations in order to solve problems. This overturns the previous assumption that reptiles only have a limited cognitive ability for finding food.
Manuel Leal, who led the study carried out at Duke University in North Carolina, said the anole's success was "completely unexpected" and "clearly demonstrates" that the lizards are capable of finding solutions.
Setting tests for lizards
Scientific opinion has always held the cognitive abilities of reptiles to be lesser than those of mammals or birds, and so any attempt to measure their skills has been rare. It was known, however, that anoles display more complex behaviour and can explore more diverse habitats than other species of reptile.
But this study, published in Biology Letters, shows that at least some species of reptile are at least as clever as their avian counterparts: a level of cognitive ability and memory that previously was never even considered.
This was achieved by testing lizards using a wooden block with two wells, one empty and one containing a worm which was covered by a cap. The lizards were then given the opportunity to pick between the holes, with the experiment then repeated but with the food in the other hole in order to see how quickly the lizards would spot the trick.
Adapting for survival
Four of the lizards were able to pass the test by either bumping or biting the cap out of the way. When the test was reversed the lizards began flipping the wrong cap but two lizards, nicknamed Plato and Socrates by the team, managed to solve the problem.
Remarkably, the lizards required fewer attempts at the test than birds, probably because the lizards' eating habits mean that they only get one chance per day, which also means that the lizards had to remember which cap the food was under for a full day each time.
Furthermore, the test clearly shows lizards adapting their behaviour in order to get to the food. "They'd put their snout under the little plastic chip and then quickly bump it," said Leal. "They don't do this in the wild".
A new dawn for reptiles?
This ability to 'unlearn' a behavioural pattern is something that some mammals have difficulty with, according to Jonathon Losos, a Harvard biologist who was not involved in the study. The results "should cause researchers to re-evaluate what they think they know about the evolution of animal cognition", Losos said.
However, scientists should be wary of declaring reptiles more cognitively advanced than birds; at least according to bird specialist Louis Lefebvre of McGill University, who also was not involved in the study.
"We know birds and mammals have bigger brains and that within bird species and within mammal species, the bigger the brain is, the higher the chance of that larger-brained species making it when moving to a new environment," Lefebvre said. "It may be the same with lizards".
Leal and his team plan to repeat the test with other species of lizards, and compare their brain and body size. This should give a more complete idea of the relation of brain size to cognitive ability in lizards.
