Inter-individual coordination in walking chimpanzees.

Humans, like many other animals, live in groups and coordinate actions with others in social settings. Such interpersonal coordination may emerge unconsciously and when the goal is not the coordination of movements, as when falling into the same rhythm when walking together. Although one of our closest living relatives, the chimpanzee (Pan troglodytes), shows the ability to succeed in complex joint action tasks where coordination is the goal, little is known about simpler forms of joint action.

Rats show direct reciprocity when interacting with multiple partners.

Direct reciprocity, where individuals apply the decision rule 'help someone who has helped you', is believed to be rare in non-human animals due to its high cognitive demands. Especially if previous encounters with several partners need to be correctly remembered, animals might either stop reciprocating favours previously received from an individual, or switch to the simpler generalized reciprocity mechanism. Here we tested the decision rules Norway rats apply when interacting with multiple partners before being able to return received help.

The smell of cooperation: rats increase helpful behaviour when receiving odour cues of a conspecific performing a cooperative task.

Reciprocity can explain cooperative behaviour among non-kin, where individuals help others depending on their experience in previous interactions. Norway rats () cooperate reciprocally according to direct and generalized reciprocity. In a sequence of four consecutive experiments, we show that odour cues from a cooperating conspecific are sufficient to induce the altruistic help of rats in a food-exchange task.

Anybody watching? How others affect helpful actions.

A new study by Havlik et al. (Science Advances, 6(28), eabb4205, 2020) reveals that rats are less likely to help a conspecific in need in the presence of passive bystanders, but that they are more likely to help when there are active bystanders that engage in helping. This study highlights the social skills of rats and the role of bystanders on cooperation, raising a range of interesting questions that should be explored both theoretically and empirically.

The social life of Norway rats ().

The Norway rat has important impacts on our life. They are amongst the most used research subjects, resulting in ground-breaking advances. At the same time, wild rats live in close association with us, leading to various adverse interactions.

Rats play tit-for-tat instead of integrating social experience over multiple interactions.

Theoretical models of cooperation typically assume that agents use simple rules based on last encounters, such as 'tit-for-tat', to reciprocate help. By contrast, empiricists generally suppose that animals integrate multiple experiences over longer timespans. Here, we compared these two alternative hypotheses by exposing Norway rats to partners that cooperated on three consecutive days but failed to cooperate on the fourth day, and to partners that did the exact opposite.

Reciprocity: Different behavioural strategies, cognitive mechanisms and psychological processes.

Reciprocity is probably one of the most debated theories in evolutionary research. After more than 40 years of research, some scientists conclude that reciprocity is an almost uniquely human trait mainly because it is cognitively demanding. Others, however, conclude that reciprocity is widespread and of great importance to many species.

Establishing an infrastructure for collaboration in primate cognition research.

Inferring the evolutionary history of cognitive abilities requires large and diverse samples. However, such samples are often beyond the reach of individual researchers or institutions, and studies are often limited to small numbers of species. Consequently, methodological and site-specific-differences across studies can limit comparisons between species.

Revisiting the possibility of reciprocal help in non-human primates.

Reciprocity is a ubiquitous and important human trait. Still, the evolutionary origin is largely unclear, partly because it is believed that our closest living relatives, other primates, do not reciprocate help. Consequently, reciprocity is suggested to have evolved in the human linage only.

Spontaneous social tool use in chimpanzees (Pan troglodytes).

Although there is good evidence that social animals show elaborate cognitive skills to deal with others, there are few reports of animals physically using social agents and their respective responses as means to an end-social tool use. In this case study, we investigated spontaneous and repeated social tool use behavior in chimpanzees (Pan troglodytes). We presented a group of chimpanzees with an apparatus, in which pushing two buttons would release juice from a distantly located fountain.

Norway rats (Rattus norvegicus) communicate need, which elicits donation of food.

Reciprocal cooperation has been observed in a wide range of taxa, but the proximate mechanisms underlying the exchange of help are yet unclear. Norway rats reciprocate help received from partners in an iterated Prisoner's Dilemma game. For donors, this involves accepting own costs to the benefit of a partner, without obtaining immediate benefits in return.

Relatedness decreases and reciprocity increases cooperation in Norway rats.

Kin selection and reciprocity are two mechanisms underlying the evolution of cooperation, but the relative importance of kinship and reciprocity for decisions to cooperate are yet unclear for most cases of cooperation. Here, we experimentally tested the relative importance of relatedness and received cooperation for decisions to help a conspecific in wild-type Norway rats (). Test rats provided more food to non-kin than to siblings, and they generally donated more food to previously helpful social partners than to those that had refused help.

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.

Experimental evidence for reciprocity in allogrooming among wild-type Norway rats.

If individuals help more those who have previously helped them, stable cooperation may ensue through alternation of roles between donors and recipients. Allogrooming, which is costly to donors and beneficial to recipients, is often exchanged between social partners. Arguably, allogrooming and allopreening are the most frequently exchanged social services and have been used as a standard model of reciprocal cooperation.