Monday, December 26, 2011


Cold-blooded cognition: Tortoises quick on the uptake

Who are you calling slow? <i>(Image: Juergen Hasenkopf/Rex Features)</i>
Who are you calling slow? (Image: Juergen Hasenkopf/Rex Features)

Tortoises aren’t noted for their speed but they are surprisingly quick-witted

"IT ALL stems from Moses," says Anna Wilkinson. Moses is her pet red-footed tortoise and a bit of a celebrity in the science world. Why? First, he outsmarted rats in a maze. Then he was the inspiration for a new lab studying reptile intelligence and the evolutionary origins of cognition. Now he has helped Wilkinson win an Ig Nobel prize. Victory for slow and steady.
This fruitful partnership began in 2004, after Wilkinson, now at the University of Lincoln, UK, started graduate school at the University of York, also in the UK. She was studying bird cognition but had earlier become fascinated by tortoises while employed in education and research at Flamingo Land zoo in North Yorkshire, UK. Although working with primates, she found herself drawn to the tortoise enclosure. Even when most of the group was basking in the sun, she recalls, at least one tortoise was exploring or feeding, and when a person walked in they all perked up, sensing that food was likely to follow. "They were always just fascinating," she says. So, a tortoise was the obvious choice as a pet.
Moses's first big academic break came in 2006. Wilkinson was attending a lecture on how rats remember their paths through a maze, when she started thinking: "Moses can do that." Afterwards, she asked the lecturer, Geoffrey Hall, if anyone had tried putting tortoises in such mazes. A literature search indicated that reptiles in general have proved pretty dim when subjected to cognitive tests. Undeterred, Hall and Wilkinson decided to see what Moses was capable of.
The pair set up a tortoise-sized test maze similar to the eight-armed radial structure used for rats and mice, then put Moses through his paces. As with the rodents he was placed in the centre of the maze and given eight chances to retrieve food from the arms - each of which had a morsel at its end. Moses quickly learned to find his way around so that he didn't revisit arms where he had already eaten the food. Like the rodents, he seemed to create a "cognitive map" from the objects he could see in the world beyond the maze. However, when Wilkinson and Hall obscured these landmarks, Moses took up a different strategy - he systematically visited the arm next to the one he had just left, allowing him to retrieve all eight food scraps (Journal of Comparative Psychology, vol 121, p 412). This flexibility of behaviour has never been seen in mammals, which seek new landmarks when old ones are removed. Clever Moses.

Ready to conquer a maze

Wilkinson and Hall were now interested in why reptiles had performed so poorly in previous cognitive studies. Taking a closer look at the reports, they found the problem. The earlier research had been done at cool temperatures, which left the cold-blooded animals feeling sluggish. Moses, by contrast, had performed at 29 °C, near the average temperature of the red-footed tortoise's native habitat in Central and South America. The warmer temperatures boosted Moses's metabolism, making him alert, lively and ready to conquer a maze.
Having finished her dissertation, Wilkinson started postdoctoral research at the University of Vienna, Austria. There, her supervisor Ludwig Huber encouraged her to pursue her interest in reptiles. In 2007 they set up the cold-blooded cognition lab. With seven more red-footed tortoises - as well as some jewelled lizards - they were ready to find out just how smart reptiles are.
One skill Wilkinson and Huber were keen to explore was gaze-following. The ability to look where another individual is looking is important because it can alert you to potential predators, or food. It is also a complex behaviour, which requires understanding that another animal's gaze can convey useful information, working out where it is looking and turning to focus on the same spot. Gaze-following has long been thought of as a talent exclusive to primates, but recently it has been found in goats and a few birds. It turns out that red-footed tortoises can do it too.
When Huber and Wilkinson shone a laser pointer at an overhead screen to attract the attention of one tortoise, they found that another individual, behind the screen, also looked up (Animal Cognition, vol 13, p 765).
Gaze-following had never been tested in reptiles before. The fact that red-footed tortoises can do it was surprising, given that they are usually solitary in the wild so may not be expected to evolve the ability to take cues from others.
Their performance on a second task was even more intriguing. The researchers found tortoises can learn to find hidden food by watching another tortoise walk around a wall to collect a treat (Biology Letters, vol 6, p 614). This indicates that tortoises are capable of social learning, a trait thought to have evolved as a special cognitive adaptation in social animals. The discovery raises the possibility that social learning may simply be an extension of general learning capabilities rather than a specialist skill.
Moses and his pals have done much to raise the intellectual standing of tortoises, but there is one test they famously failed. Contagious yawning is thought to arise from empathy, but Wilkinson doubted this theory. She spent six months teaching one tortoise to yawn in the hope that others would learn the trick - even though tortoises lack empathy. The yawns stubbornly refused to spread, Wilkinson and Huber reported in a paper that earned them the Ig Nobel prize earlier this year (Current Zoology, vol 57, p 477).
Wilkinson's work is helping revive interest in reptile cognition, says Gordon Burghardt at the University of Tennessee at Knoxville. This is important because most research on animal cognition has been on mammals or birds. Reptiles split from those groups more than 250 million years ago, so studies of how they think can shed light on the evolutionary roots of animal intelligence. Burghardt recently found "surprisingly advanced" social learning in pond turtles, a more social group than tortoises. Meanwhile, Manuel Leal and Brian Powell at Duke University in Durham, North Carolina, have found that tree-dwelling anole lizards from Puerto Rico can solve simple problems to find food - a behaviour previously seen only in birds and mammals.
Reptiles are clearly far smarter than we thought. Wilkinson has one explanation - at least for Moses and his ilk. Tortoises receive no care after they hatch, so they have to learn on their own, she points out. And with a very high attrition rate, there is strong natural selection for intelligence. "They learn things very fast because they have to do so to survive," she says. "They are learning machines."

Jeff Hecht is a consultant with New Scientist


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