From ScienceDaily: Norway rats trade different commodities

Researchers of the University of Bern have shown for the first time in an experiment that also non-human animals exchange different kind of favours. Humans commonly trade different commodities, which is considered a core competence of our species. However, this capacity is not exclusively human as Norway rats exchange different commodities, too. They strictly follow the principle “tit for tat” — even when paying with different currencies, such as grooming or food provisioning.

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In an experimental study, Manon Schweinfurth and Michael Taborsky from the Institute of Ecology and Evolution of the University of Bern tested whether common Norway rats engage in reciprocal trading of two different forms of help, i.e. allogrooming and food provisioning. Their test rats experienced a partner either cooperating or non-cooperating in one of the two commodities. To induce allogrooming, the researchers applied saltwater on the test rats’ neck, which is hardly accessible to self-grooming, so help by a partner is needed.

To induce food provisioning, partner rats could pull food items towards the test rats. Afterwards, test rats had the opportunity to reciprocate favours by the alternative service, i.e. allogrooming the partner after receiving food from it, or donating food after having been allogroomed. The test rats groomed more often cooperating than non-cooperating food providers, and they donated food more often to partners that had heavily groomed them before. Apparently, they traded these two services among another according to the decision rules of direct reciprocity.

“This result indicates that reciprocal trading among non-human animals may be much more widespread than currently assumed. It is not limited to large-brained species with advanced cognitive abilities,” says Manon Schweinfurth.

As is usually the case with ScienceDaily, the text is based upon the University’s press release, and it takes a bit of digging to find the actual paper, which is in Current Biology.

Reciprocal Trading of Different Commodities in Norway Rats

The prevalence of reciprocal cooperation in non-human animals is hotly debated [1, 2]. Part of this dispute rests on the assumption that reciprocity means paying like with like [3]. However, exchanges between social partners may involve different commodities and services. Hitherto, there is no experimental evidence that animals other than primates exchange different commodities among conspecifics based on the decision rules of direct reciprocity. Here, we show that Norway rats (Rattus norvegicus) apply direct reciprocity rules when exchanging two different social services: food provisioning and allogrooming. Focal rats were made to experience partners either cooperating or non-cooperating in one of the two commodities. Afterward, they had the opportunity to reciprocate favors by the alternative service. Test rats traded allogrooming against food provisioning, and vice versa, thereby acting by the rules of direct reciprocity. This might indicate that reciprocal altruism among non-human animals is much more widespread than currently assumed.

As the summary of the paper shows, the press release was overselling the unique human aspect of reciprocity using different commodities. This behavior have been observed in other primates. This study, however, is the first to show the behavior outside primates.

I always find it interesting when a study shows that a trait that is presumed to be unique for humans, or primates, actually exist among other animals. It makes you wonder if the reason why the traits are considered unique among humans/primates, is because we simply haven’t looked for them before.