Charles Darwin considered the apparently widespread occurrence of ‘altruistic’ behaviour in the animal kingdom as one of the most important test cases for his theory of evolution by natural selection. The evolution of cooperative behaviour has somehow remained enigmatic to the students of biology until the development of kin selection theory by William D. Hamilton in 1967. This theory inspired research into the origin and maintenance of cooperative behaviour in a wide range of animal taxa. Cooperative behaviour has been shown to provide individuals with either direct fitness benefits (e.g. mutualism, reciprocity) or indirect benefits (e.g. helping kin to raise offspring). Alternatively, helpful behaviour may be elicited by enforcement or deception, with negative fitness consequences to the cooperator.
Natural selection of cooperation:
Among the selection mechanisms responsible for the emergence and evolutionary stability of cooperation, the concept of ‘reciprocal altruism’ addresses an evolutionary enigma: it aims to explain how helpful behaviour can be selected despite immediate costs to the helper exceeding its immediate benefits, if this is not compensated by indirect fitness benefits. The solution of this riddle involves future returns: the execution of help increases the likelihood that help will be received conversely. Compared to the functionality of kin selection, if cooperation is based on reciprocity ‘shared genes’ between social partners are replaced by a ‘shared future’, likewise resulting in aligned fitness interests. The evolution of such exchange of services is hampered by the inherent temptation to cheat, which largely disappears, however, if the pay-offs of social partners are correlated, for instance because they repeatedly interact again in the future. An intriguing question is which evolved decision rules animals apply to exchange goods and services among each other without running the risk of being exploited by their social partners.
As model organisms to address this question we use wild-type Norway rats (Rattus norvegicus). These highly social animals live in large colonies of both related and unrelated individuals. Especially females show complex social behaviour, including allogrooming, communal nursing, as well as food hoarding and sharing. Using a manual food-exchange task, we have shown that female rats differ in their propensity to cooperate according to previous social experiences. Particularly, they provide help to a partner from which they have received help before (direct reciprocity) and are in general more cooperative to any individual after experiencing help by a conspecific (generalised reciprocity). They exchange different commodities among each other, adjust the help they provide to a partner to the quantity and quality of help previously received, and their helpfulness takes both own costs and the receiver's benefits into account. For this they use chemical communication to signal helpfulness and to assess the need of their social partner.
Principal investigator: Michael Taborsky
Kettler, N., Schweinfurth, M.K., Taborsky, M. 2021. Rats show direct reciprocity when interacting with multiple partners. Sci. Rep. 11: 3228 [PDF]
Schneeberger, K., Röder, G., Taborsky, M. 2020. The smell of hunger: Norway rats provision social partners based on odour cues of need. PLoS Biol 18(3): e3000628 [PDF]
Schweinfurth, M.K. & Taborsky, M., (2018a) Reciprocal trading of different commodities in Norway rats. Curr. Biol. 28, 594–599 [PDF]
Schweinfurth M.K. & Taborsky M. (2018b) Relatedness decreases and reciprocity increases cooperation in Norway rats. Proc. R. Soc. B 285: 20180035 [PDF]
Rutte C. & Taborsky M. (2007): Generalized reciprocity in rats. PLoS Biol. 5:1421-1425 [PDF]