Reciprocal cooperation in rats
We use wild-type Norway rats to study under which circumstances cooperative behaviour can establish within an animal population. Rats are highly social, nest communally, store food and groom eachother. We train them to perform a task where they can produce food for a social partner by pulling a tray towards the cage so that the partner can reach a food reward.
Rats preferentially help partners from which they have received help before (direct reciprocity). Thus, when helping an other individual, they can expect to get help back during a future encounter.
Costs and benefits
Theoretical models frequently include costs for the donors and benefits for the receiver as important parameters for reciprocal cooperation. However, how they affect the decision of animals whether to help or not was largely unknown. We therefore varied the hunger status of the partner as well as the resistance of the tray to be pulled by the focal rat in order to increase both benefits of the food reward as well as the costs for the donor to perform the cooperative task.
The rats took more costs into account when helping an individual from which they have received help before. Furthermore, they produced more food for hungry partners, especially if they already had a low body weight and thus were in higher need. So far, it was assumed that only humans are able to judge the relative benefit of help for a partner, but this experiment on rats give hints that other animals take it into account as well.
The partner rats show various behaviour to solicitate help during the experiment, such as reaching for the reward, running up and down in front of the donor and emitting ultrasonic calls. However, such behaviour can be manipulative and thus not represent true need. Rats are nocturnal animals and use smell as important source of information. We thus tested whether rats can judge the hunger status of a partner by smell alone. Indeed, when the focal rats only received the odour of a partner, excluding all other cues, they still provided more help for a hungry than for a satiated individual. We thus assume that odour may honestly communicate need in rats and give reliable information about the benefit of help for a social partner.
Schmid R., Schneeberger K., Taborsky M. (2017) Feel good – do good? Disentangling reciprocity from unconditional prosociality. Ethology, accepted
Schweinfurth M. K., Neuenschwander J., Engqvist L., Schneeberger K., Rentsch A. K., Gygax M., Taborsky M. (2017) Do female rats form social bonds? Behavioral Ecology and Sociobiology, accepted
Schneeberger K., Dietz M., Taborsky M. (2012) Reciprocal cooperation between unrelated rats depends on cost to donor and benefit to recipient. BMC Evolutionary Biology 12 (1): 41 [pdf]