Degus are highly social, intelligent rodents native to the highlands of Chile. They adorn the openings of their burrows with piles of sticks and stones, have bubbly personalities and like to play games.
But in a laboratory setting, degus can do much more than play hide-and-seek, according to a study in the online journal Plos One (www.plosone.org). They can learn to use tools.
Specifically, degus have been trained to reach through a fence, grab hold of a tiny rake and pull their favorite food, half a peeled sunflower seed, close enough to reach with their mouths. After two months of practice, researchers say, the degus can move the rake as smoothly and efficiently as croupiers in any Las Vegas casino.
This is first time rodents have been trained to wield tools, said Atshushi Iriki, a neuroscientist, who led the experiments at the Laboratory for Symbolic Cognitive Development at the Riken Institute in Tokyo. But other species may soon join them.
While it has long been thought that tool use is a hallmark of higher intelligence, Dr. Iriki said, the brain structures that underlie such abilities may lie dormant in many animals with good hand-and-eye or paw-and-eye coordination. Training them to use tools in captivity provides insights into the plasticity of their brains, he said, and may shed light on how early humans evolved tool use in the first place.
''There's an interesting push-pull to this demonstration of the use of an artificial rake by a rodent,'' said Richard Morris, a neuroscientist and expert on animal behavior at the University of Edinburgh, who was not involved in the study. ''The push is that if rodents no less than primates can learn to use tools, interesting questions arise about the nature and components of intelligence. And the pull part is that the observation sets the stage for a new neurobiological approach to this fundamental facet of mind, of brain.''
In the wild many animals use simple tools. Chimpanzees and crows actually create them. But an underlying question is, What changes take place in an animal brain when tool use evolves?
To find out, Dr. Iriki initially conducted experiments with Japanese macaques, monkeys that do not tend to use tools in the wild. In the laboratory, he trained them to use a rake to reach out and retrieve their favorite treat, raisins. Later the animals learned to use a short rake to pull in a longer rake, which could then be used to fetch more distant raisins.
As the monkeys developed these skills, their brains showed signs of gene activity in a brain region that integrates vision and touch. The same was likely to be true of the degu, Dr. Iriki said. The rodent has superb paw-and-eye coordination and a pad on its paw that can act like a thumb.
In the experiments, six degus stood behind a fence with gaps wide enough to let their forelegs pass through but not their mouths. A rake-like tool was placed within easy reach. The animals had to grasp the rake and pull seeds in close enough to eat.
As the degus became more adept, the experimenters placed the seeds further away. The animals had to push the rake around the seed, twist it and pull.
The degus did not hesitate to use rakes of different sizes, colors and shapes. They were reluctant to use a tool that had no teeth.
Studies are under way to see if the degu's brain reorganized in response to tool use, Dr. Iriki said.
Meanwhile, the researchers have begun a new set of experiments with marmosets, a small primitive primate, to see if their brains show similar molecular and genetic changes with tool use.