Rats given a helping paw are more prone to helping others--even complete strangers. This suggests that the animals' social life may be richer than we thought, according to the researchers whose new study revealed this rodent altruism.
Many animals, including rats, demonstrate direct reciprocity--described as "I'll help you if you help me." But generalized reciprocity, in which individuals remember how they were treated in the recent past and apply it to others, including strangers, was thought to be a uniquely human trait, explains behavioral ecologist Claudia Rutte at the University of Lausanne in Switzerland. However, she notes, previous studies haven't specifically looked for generalized reciprocity in other animals.
To find out if rats have this capacity, Rutte and Michael Taborsky of the University of Bern in Switzerland trained rats to pull a lever that would deliver an oat flake reward to another rat on the other side of a wire mesh wall in a shared cage. Some of these rats were then put on the receiving side, paired for several days with either other rats trained to be helpful—-three different ones over the span--or with untrained rats that didn't pull the lever and provide food. After several days of living with such generous or not-so-generous neighbors, these test rats were then switched back to the lever side of the cage, paired with a new neighbor rat, and watched to see if they would provide food for it. Rats who had been paired with food-providing neighbors helped their new partner more often than those who had had unhelpful neighbors, the researchers report online this week in Public Library of Science Biology. Rutte's team also found that when a test rat was paired with one of the rats that had earlier provided it with oak flakes, it pulled the food lever even more--showing direct reciprocity. When the cage was empty of any neighbor rat, it barely pulled the food lever at all.
In a pack of 200 rats, where it's hard to remember who's been helpful and who hasn't, a general willingness to help others makes sense as a strategy, Rutte says. "It may be a mechanism for how cooperation can evolve when you cannot recognize your partner," she says, noting that rats are notoriously bad at remembering other individuals.
"It's a new way of explaining the cooperation we see," says Jeff Stevens, a comparative psychologist at Max Planck Institute in Leipzig, Germany, adding that such helpfulness avoids needing to remember one's friends. Nicola Clayton, who studies comparative cognition at the University of Cambridge, U.K., suggests looking into the prevalence of generalized reciprocity among social and nonsocial animals to help our understanding of the evolution of cooperation.
)
)
)
)
)
)
)
)
