Reciprocal allogrooming among unrelated Norway rats (Rattus
norvegicus) is affected by previously received cooperative, affiliative
and aggressive behaviours
Manon Karin Schweinfurth
Received: 5 June 2017 /Revised: 7 November 2017 /Accepted: 15 November 2017
Springer-Verlag GmbH Germany, part of Springer Nature 2017
Reciprocity can generate stable levels of cooperation among unrelated social partners. If individuals interact repeatedly, costs of altruistic acts can
be compensated through an exchange of donor and receiver roles. Frequent interactions are conducive to attaining evolutionarily stable
reciprocal exchange. High interaction frequencies are typical for group members maintaining close relationships among one another, which
may thereby facilitate reciprocity. Norway rats (Rattus norvegicus) are highly social animals that were experimentally shown to reciprocally
exchange food donations and allogrooming. Here, we tested experimentally the relationship between reciprocal cooperation and other social
behaviours exchanged within dyads of wild-type Norway rats. In particular, we asked whether and how interactions differing in quality
(characterised by affiliative and aggressive behaviours) influence reciprocal exchanges of different social services. Our experiment involved
three steps: Focal individuals experienced social partners that were either providing them with food or not, via a learnt stick-pulling task.
Thereafter, they could either interact physically with these partners, or not. Subsequently, we induced allogrooming among them by applying
saltwater to an inaccessible part of the body, and tested for the reciprocation of allogrooming. When individuals were allowed to interact freely,
previously cooperative food providers exhibited more aggression towards focal individuals than previously uncooperative partners, which might
reflect an attempt to coercively demand a return of food provisioning from focal rats. Higher frequencies of affiliative behaviours and lower
frequencies of aggressive behaviours experienced during the unrestricted interaction phase tended to increase the focal rats’ propensity to
engage in grooming the partner in the subsequent induced allogrooming phase. This suggests that affiliative and aggressive behaviours affect
the allogrooming propensity of rats. In particular, higher frequencies of received aggression decreased the propensity to reciprocate previously
received cooperation. We provide experimental evidence that rats are more likely to groom partners that pulled a stick to deliver food to them.
Reciprocal exchange of allogrooming depends apparently on experienced cooperation, but also on the quality of the social relationship.
Close social relationships among individuals may enhance reciprocal exchange of services and thereby ensure long-term cooper-
ation. Thus, we tested whether in unrelated and previously unfamiliar Norway rats, the quality of social interactions, that is, the
amount of exchanged affiliative and aggressive behaviours, affects reciprocal cooperation, and whether received cooperation in turn
predicts subsequent social behaviour. Our results show that focal individuals are generally more helpful to previously helpful
partners, but that the quality of social interactions may modify their decision to cooperate. Received aggressive and affiliative
behaviours affected the subsequent reciprocal exchange of hygienic behaviour. Moreover, received food provisioning affected the
exchange of cooperative, affiliative and aggressive behaviours also outside of a food-provisioning context. These data reveal a close
relationship between the exchange of social behaviours between individuals and their propensity to cooperate with one another.
Keywords Norway rats
Behaviours by which an actor benefits a receiver whilst pay-
ing immediate costs are referred to as altruistic (Wilson 1975).
The establishment of evolutionarily stable levels of altruism
Communicated by R. Noë
* Binia Stieger
Behavioural Ecology Division, Institute of Ecology and Evolution,
University of Bern, Wohlenstrasse 50a,
CH-3032 Hinterkappelen, Switzerland
Behavioral Ecology and Sociobiology (2017) 71:182