Whom to help, how and why? Reciprocal trading among Norway rats

Supervisor: Michael Taborsky

External examiners: Hanno Würbel & Frans de Waal

Cooperation, i.e. when one individual helps another, is widespread in nature. The evolution of cooperation is not easy to explain because why should someone help someone else instead of selfishly keeping the resources? One possibility is to exclusively help relatives that share some genes. Thereby helpers receive a benefit by transferring their genes indirectly to the next generation.  However, help is not restricted to kin. Reciprocity, which can be illustrated by the rule "I help you because you helped me", is one explanation, but it is probably the most disputed explanation. During my PhD, I aimed at unveiling behavioural mechanisms underlying reciprocity by using small-brained but highly social Norway rats (Rattus norvegicus). Working with rats allowed me to test frequent assumptions that are assumed to limit reciprocal cooperation in non-human animals. Please find some examples below.

Evidence for reciprocal cooperation comes from both experimental and observational studies. However, these approaches have been criticised due to artificial contexts or the lack of causality. Therefore, I designed an experimental study to test whether a non-artificial behaviour, allogrooming, follows the causal rules of reciprocity.

A frequent assumption of reciprocal cooperation is that only a single commodity is exchanged. However, it seems more likely that in a natural context, different commodities are traded against each other, which I tested experimentally.

One of the central questions regarding the evolutionary mechanisms underlying cooperation is the relative importance of kin selection and reciprocity. Many social animals live in groups that consist at least partly of related individuals. This has led to the common assumption that cooperation in such groups might be better explained by kin selection than by reciprocal cooperation. Thus, I tested the interplay between the effects of relatedness and reciprocity.

Reciprocation of received help may be based either on a single experience with a partner or on long-term relationships, involving social bonds. However, the relative importance of social bonds and of recent encounters is largely unclear. In a series of experiments, I aimed to clarify the relative importance of those two mechanisms for cooperation in Norway rats.

Negotiation about the amount of help can stabilise cooperation levels. Thus, communication is an important component of cooperative interactions. I tested whether rats communicate their need, and how partners respond to this.

In summary, I conclude from my PhD thesis that reciprocity is potentially more ubiquitous than believed. More information about the projects can be found here.

© Manon Schweinfurth

I would like to thank the Swiss National Science Foundation for funding this project!