Cooperative intentions and their implications on reciprocal cooperation in Norway rats

Funding: This study was financially supported by the Swiss National Science Foundation, grant number 31003A_156152, which was awarded to Michael Taborsky.One way to cooperate with others and avoid exploitation is reciprocal cooperation. Reciprocity is the selective helping of those who were cooperative before, which is commonly based on outcomes. Yet, outcomes may not reflect intentions, i.e., if an individual is unable but willing to help. Humans, including children, show such intention-based reciprocity. However, it is unclear whether other animals consider intentions in reciprocal settings. Here, I tested whether Norway rats (Rattus norvegicus) reciprocate help based on intentions by manipulating the outcome while keeping the partner’s cooperative inten-tions the same. Subjects experienced a partner that was able to help by providing food via a movable platform. In another condition, the same partner was unable to help because the platform was blocked. When the roles were exchanged afterwards, subjects provided food more often to ‘able’ than ‘unable’ partners, even though the latter attempted to help. I compare these findings to data using ‘willing’ and ‘unwilling’ partners that were able to help. Again, rats based their cooperative behaviour on outcomes rather than the intention to help. This suggests that rats reciprocate primarily based on outcomes and seem to not consider cooperative intentions. Although, subjects provided consistently less food to partners that did not help, they provided them with some help. Potentially, rats use a cognitively less demanding strategy by helping defectors a bit to maintain cooperation. Thereby, cooperation might be resistant to situations in which an apparent defector was actually unable to help, but had cooperative intentions, and might be a good cooperation partner in the future.Publisher PDFPeer reviewe

Reciprocal cooperation - Norway rats (Rattus norvegicus) as an example

The Swiss National Science Foundation provided funding (P2BEP3_175269).Many animals cooperate even with unrelated individuals in various contexts, like providing food or allogrooming others. One possibility to explain the evolution of such apparently altruistic behaviour is reciprocity. In reciprocal cooperative interactions, individuals help those partners that have been previously cooperative and therefore exchange favours. This conditional help follows rules like “I help you because you helped me.” These rules are often assumed to be so cognitively demanding that they may be limited to humans. In this chapter, I will shed light on the cognitive underpinnings of reciprocal cooperation by reviewing work on one of the yet best-studied animal in this research area, the Norway rat (Rattus norvegicus). Various studies have demonstrated that Norway rats reciprocally exchange different goods and services. They most likely form attitudes toward social partners that are based on the cooperation level of the last encounter, which they remember over long time spans. Cooperation decisions based on attitudes appear cognitively less complex than calculations of received and given favors. Thus, reciprocal cooperation based on this cognitive mechanism might be in fact more widespread among nonhuman animals than commonly believed.PostprintPeer reviewe

The social life of Norway rats (Rattus norvegicus)

This work was supported by a grant of the Swiss National Science Foundation (grant number P2BEP3 175269).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. In face of this relevance, it is surprising how little is known about their natural behaviour. While recent laboratory studies revealed their complex social skills, little is known about their social behaviour in the wild. An integration of these different scientific approaches is crucial to understand their social life, which will enable us to design more valid research paradigms, develop more effective management strategies, and to provide better welfare standards. Hence, I first summarise the literature on their natural social behaviour. Second, I provide an overview of recent developments concerning their social cognition. Third, I illustrate why an integration of these areas would be beneficial to optimise our interactions with them.Publisher PDFPeer reviewe

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

Funding was provided by SNF-grant 31003A_156152 to M.T. and P2BEP3 175269 to M.K.S.Theoretical models of cooperation typically assume that agents use simple rules based on last encounters, such as “tit-for-tat”, to reciprocate help. In 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. In additional controls, focal rats experienced cooperating and defecting partners only once. In a bar-pulling setup, focal rats based their decision to provide partners with food on last encounters instead of overall cooperation levels. To check whether this might be due to a lack of memory capacity, we tested whether rats remember the outcome of encounters that had happened three days before. Cooperation was not diminished by the intermediate time interval. We conclude that rats reciprocate help mainly based on most recent encounters instead of integrating social experience over longer timespans.PostprintPeer reviewe

Capuchins (Sapajus apella) and their aversion to inequity

Funding: Authors would like to acknowledge the financial support we received from the European Research Council (Synergy grant 609819 SOMICS provided to Josep Call) and the Swiss National Science Foundation (P2BEP3 175269 provided to Manon K. Schweinfurth).Humans have a strong sense of fairness and are usually averse to unequal treatment for the same action. Ever since Brosnan and de Waal showed a similar effect in capuchin monkeys (Sapajus apella), numerous studies using different experimental methods have been conducted to investigate whether animals show inequity aversion like humans do. Capuchin monkeys have become one of the best-studied animals in this area. Our first aim in this chapter was to synthesise the findings in this literature. We found that there is mixed evidence for inequity aversion in capuchin monkeys. Our second aim was to understand this variation by focusing on the following factors: the type of task used, the feeding regime outside the experiment and the monkeys’ social environment. To obtain data on some of these factors, as they are not always reported in published studies, we contacted researchers in the main laboratories conducting this work. We found that responses to inequity systematically varied as a function of the task demands and the feeding regime, but not the social environment. Tasks, in particular pulling tasks, that required participants to expend effort to get the food were more likely to detect evidence of inequity aversion. Moreover, monkeys with access to food before or after testing, were more likely to show inequity aversion than those whose access to food was temporarily restricted. We note that our survey is an explorative approach to investigate the variation in reports on inequity aversion in capuchin monkeys. We hope this chapter raises awareness of the complexity of the concept and generates new testable hypotheses, which might advance our understanding of the theoretical foundations of inequity aversion.PostprintPeer reviewe

On closer inspection : reviewing the debate on whether fish cooperate to inspect predators

This work was funded by an EASTBIO DTP scholarship to A. Li Veiros.Cooperative behaviours, which benefit a recipient, are widespread in the animal kingdom; yet their evolution is not straightforward. Reciprocity, i.e., cooperating with previously experienced cooperative partners, has been suggested to underly cooperation, but has been contested throughout the years. Once a textbook example of reciprocity was cooperative predator inspection, where one or several individuals leave their group to approach a potential threat. Each can at any point stop or retreat, increasing the risk for its partner. It was suggested that inspecting individuals follow a specific reciprocal strategy called tit-for-tat, i.e., cooperating on the first move and then copying the partner's last move. Numerous studies provide evidence to support the claim that fish cooperate to inspect predators, including three-spined sticklebacks (Gasterosteus aculeatus), guppies (Poecilia reticulata) and minnows (Phoxinus phoxinus). However, over the past few decades some scholars have expressed scepticism whether predator inspection is indeed a cooperative behaviour or rather a case of by-product mutualism, which describes behaviours that benefit a partner as a corollary of an otherwise selfish behaviour. For instance, it has been shown that pairs of fish moving in unfamiliar environments appear to coordinate movements even in the absence of predators. Many studies have also used coarse measures of overall approach rates towards predators rather than the fine-grained analyses necessary to infer tit-for-tat in cooperative inspections. Now is the time to return to the question of cooperative predator inspection with new tools and approaches to resolve a decades-old debate.Publisher PDFPeer reviewe

Male Norway rats cooperate according to direct but not generalized reciprocity rules

Funding was provided by the Swiss National Science Foundation grants 31003A_156152 and 31003A 176174 to M.T. and P2BEP3 175269 to M.K.S.Reciprocal cooperation may evolve if the costs of help are reliably compensated for by delayed returns provided in future interactions. The associated probabilities and cost–benefit ratios may vary systematically between the sexes, which often display different dispersal strategies and interaction patterns. Whereas female Norway rats, Rattus norvegicus, are known to apply direct and generalized decision rules of reciprocal cooperation, the rules according to which males reciprocate favours are less well understood. Therefore, we investigated the cooperation propensity of male wild-type Norway rats. Male test rats experienced cooperating partners that provided food to them, or defecting partners that refused to provide help. Afterwards, test rats could donate food to previously experienced or unknown partners, resembling direct and generalized reciprocity paradigms, respectively. Male rats cooperated according to direct reciprocity, suggesting that this decision rule is similarly important for both sexes. However, whereas females additionally help according to generalized reciprocity, males did not apply this rule. These results suggest a sex difference in reciprocal decision rules, highlighting the potential importance of different interaction patterns and cost–benefit ratios between the sexes.PostprintPeer reviewe

The transfer of alternative tasks in reciprocal cooperation

Funding was provided by SNF-grant 31003A_156152 to M.T.Direct reciprocity can establish stable cooperation. Nevertheless, the significance of this mechanism is yet unclear. A frequent assumption is that both commodity and context should be the same when help is exchanged between social partners. Yet, an exchange of different favours appears more likely in a natural setting. This is assumed to be cognitively demanding, however, because experienced help in one context needs to change the motivation to help by different means or in a different context. We tested whether Norway rats, Rattus norvegicus, transfer help from one cooperative task to another. Individuals could provide food to previously either cooperating or defecting partners by using a different mechanism to produce food for their partner than the partner had used to help them. Test subjects indeed helped previously cooperative partners more often than defecting ones by using a different provisioning mechanism. This implies that rats realize the cooperative propensity of social partners, which they consequently reward by help of a different kind; hence, they do not merely copy experienced helping behaviour. Our results suggest that animals other than primates are capable of transferring help between different contexts, which highlights new possibilities for the occurrence of reciprocal altruism involving different commodities and services in nature.PostprintPeer reviewe

Reciprocal trading of different commodities in Norway rats

Funding was provided by Swiss National Science Foundation grants 310030B_138660 and 31003A_ 156152 to M.T.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. Hitherto, there is no experimental evidence that animals other than primates exchange different commodities among conspecifics based on the decision rules of direct reciprocity. Here, we show that Norway rats (Rattus norvegicus) apply direct reciprocity rules when exchanging two different social services: food provisioning and allogrooming. Focal rats were made to experience partners either cooperating or non-cooperating in one of the two commodities. Afterward, they had the opportunity to reciprocate favors by the alternative service. Test rats traded allogrooming against food provisioning, and vice versa, thereby acting by the rules of direct reciprocity. This might indicate that reciprocal altruism among non-human animals is much more widespread than currently assumed.PostprintPeer reviewe

Reciprocity : different behavioural strategies, cognitive mechanisms and psychological processes

The Swiss National Science Foundation provided funding to MKS (grant number P2BEP3 175269). The European Research Council provided funding to JC (Synergy grant 609819 SOMICS).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 wide-spread and of great importance to many species. Yet, it is unclear how these species reciprocate, given its apparent cognitive complexity. Therefore, our aim was to unravel the psychological pro-cesses underlying reciprocity. By bringing together findings from studies investigating different aspects of reciprocity, we show that reciprocity is a rich concept with different behavioural strate-gies and cognitive mechanisms that require very different psychological processes. We reviewed evidence from three textbook examples, i.e. the Norway rat, common vampire bat and brown capuchin monkey and show that the species use different strategies and mechanisms to recipro-cate. We continue by examining the psychological processes of reciprocity. We show that the cog-nitive load varies between different forms of reciprocity. Several factors can lower the memory demands of reciprocity such as distinctiveness of encounters, memory of details and network size. Furthermore, there are different information operation systems in place, which also vary in their cognitive load due to assessing the number of encounters and the quality and quantity of help. We conclude that many species possess the psychological processes to show some form of reciprocity. Hence, reciprocity might be a widespread phenomenon that varies in terms of strategies and mechanisms.Publisher PDFPeer reviewe