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Antisocial Tortoises Learn From Each Other

30 March 2010 8:01 pm
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Birds do it, monkeys do it, humans do it-learning from the individuals around you is a crucial skill if you want to survive in a group. Scientists have thought that the ability to learn from others evolved in step with communal living. Now a study demonstrates an exception: A solitary reptile is an adept social learner.

From the time young red-footed tortoises (Geochelone carbonaria) hatch in their native South American rainforests, they are alone. They grow up without parents or siblings, and adults rarely cross paths. If a head-bobbing display determines that a stranger is of the opposite sex, the two will mate perfunctorily-otherwise they just ignore each other.

In a species so uninterested in social interactions, it's hard to see how the ability to learn from others could have evolved, says Anna Wilkinson, a cognitive biologist at the University of Vienna. But one day she scattered dandelions, a favorite snack, near a female tortoise named Wilhelmina, who began to eat. A second tortoise ignored a clump that had fallen near him and followed Wilhelmina to her clump instead. This made Wilkinson wonder whether the second tortoise had "learned that the dandelions were there" by observing where Wilhelmina was eating.

So Wilkinson set out to test whether tortoises learned a navigation task better by watching other tortoises or on their own. She set up a v-shaped wire fence and placed a bowl containing a few tidbits of strawberry and mushroom inside the fence at the point of the "V". Then she set Wilhelmina outside the tip of the "V", with the treats on the other side of the fence. In 12 trials, Wilhelmina tried to force her way through the barrier but never tried to walk around. The same was true of three other control tortoises Wilkinson and her colleagues tested. "In later trials, they would ... go up the arm [of the "V"] and go to sleep," says Wilkinson.

She then slowly and patiently trained Wilhelmina to navigate the fence-it took more than 150 trials. But when she tested four tortoises after letting them watch Wilhelmina complete the maneuver, two succeeded on their first try, one made it after watching the demonstration a second time, and the fourth tortoise had to watch Wilhelmina nine times, Wilkinson and her colleagues will report online tomorrow in Biology Letters.

Social learning "is considered an advanced skill and a root of culture. ... These guys shouldn't be able to do it, and they can," says Wilkinson . The result suggests that social learning, rather than a unique ability that evolved in social animals because it makes them more successful in group living, is simply another dimension of general learning, which depends only on an animal's cognitive abilities, Wilkinson says.

The fact that it took so long to train Wilhelmina, whereas tortoises who watched the demonstration could learn the maneuver much more quickly, is the best piece of evidence against the hypothesis that the evolutionary pressures of group living sharpened social learning in gregarious species, says Jennifer Templeton, an ecologist at KnoxCollege in Galesburg, Illinois. Although the results challenge the hypothesis, "I just don't think they challenge it very well," Templeton says. To disprove it, the researchers would have to show that the tortoises that watched Wilhelmina didn't simply have more environmental clues telling them how to complete the task, something Templeton doubts.

But Louis Lefebvre, an animal behaviorist at McGill University in Montreal, Canada, argues that "there's been evidence for a long time" against the hypothesis that learning from others is a novel ability that evolved separately from other types of learning. "Information in the environment is information in the environment, whether it's given to you by an animal" or not, he says. "This study confirms it in a nice way."

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