Reciprocal Trading of Different Commodities in Norway Rats

An exploratory study of behavioral traits and the establishment of social relationships in female laboratory rats

There is growing evidence that social relationships influence individual fitness through various effects. Clarifying individual differences in social interaction patterns and determinants for such differences will lead to better understanding of sociality and its fitness consequences for animals. Behavioral traits are considered one of the determining factors of social interaction. The purpose of this study was to explore the effects of individual behavioral traits on social relationship building in laboratory rats (Rattus norvegicus), a highly social species. Initially, the following behavioral characteristics were measured in individuals: tameness (glove test), activity (open field test), exploration (novel object test), sociability (three-chamber test), and boldness (elevated plus maze test). We then used DeepLabCut to behaviorally track three groups of four individuals (12 total) and analyze social behaviors such as approach and avoidance behaviors. Principal component analysis based on behavioral test results detected behavioral traits interpreted as related to exploration, boldness, activity, and tameness, but not sociability. In addition, behavioral tracking results showed consistent individual differences in social behavior indices such as isolation time and partner preference. Furthermore, we found that different components were correlated with different phases of social behavior; exploration and boldness were associated with the early stages of group formation, whereas activity was associated with later stages of relationship building. From these results, we derived hypothesize that personality traits related to the physical and social environment have a larger influence in the relationship formation phase, and the behavioral trait of activity becomes important in the maintenance phase of relationships. Future studies should examine this hypothesis by testing larger group sizes and ensuring there is less bias introduced into group composition.

Assessment of help value affects reciprocation in Norway rats

Wild-type Norway rats reciprocate help received in a well-replicated experimental food-giving task, but the criteria to appraise the received help's value are unclear. We tested whether quality or quantity of received help is more important when deciding to return help, and whether partner familiarity and own current need affect this evaluation. We experimentally varied recipients of help's hunger state, and familiar or unfamiliar partners provided either higher caloric food (enhanced quantity; carrots) or food higher in protein and fat (enhanced quality; cheese). Reciprocation of received help was our criterion for the rats' value assessment. Familiarity, food type and hunger state interacted and affected help returned by rats. Rats returned less help to familiar partners than to unfamiliar partners. With unfamiliar partners, rats returned more help to partners that had donated preferred food (cheese) than to partners that had donated less preferred food (carrots), and they returned help earlier if they were satiated and had received cheese. With familiar partners, food-deprived rats that had received cheese returned more help than satiated rats that had received carrots. Our results suggest that Norway rats assess the received help's value based on its quality, their current need and partner familiarity before reciprocating received help.

Sharing Positive Affective States Amongst Rodents

Group living is thought to benefit from the ability to empathize with others. Much attention has been paid to empathy for the pain of others as an inhibitor of aggression. Empathizing with the positive affect of others has received less attention although it could promote helping by making it vicariously rewarding. Here, we review this latter, nascent literature to show that three components of the ability to empathize with positive emotions are already present in rodents, namely, the ability to perceive, share, and prefer actions that promote positive emotional states of conspecifics. While it has often been argued that empathy evolved as a motivation to care for others, we argue that these tendencies may have selfish benefits that could have stabilized their evolution: approaching others in a positive state can provide information about the source of valuable resources; becoming calmer and optimistic around animals in a calm or positive mood can help adapt to the socially sensed safety level in the environment; and preferring actions also benefiting others can optimize foraging, reduce aggression, and trigger reciprocity. Together, these findings illustrate an emerging field shedding light on the emotional world of rodents and on the biology and evolution of our ability to cooperate in groups.

Neural mechanisms of comforting: Prosocial touch and stress buffering

Comforting is a crucial form of prosocial behavior that is important for maintaining social unity and improving the physical and emotional well-being of social species. It is often expressed through affiliative social touch toward someone in distress, providing relief for their distressed state. In the face of increasing global distress, these actions are paramount to the continued improvement of individual welfare and the collective good. Understanding the neural mechanisms responsible for promoting actions focused on benefitting others is particularly important and timely. Here, we review prosocial comforting behavior, emphasizing synthesizing recent studies carried out using rodent models. We discuss its underlying behavioral expression and motivations, and then explore both the neurobiology of prosocial comforting in a helper animal and the neurobiology of stress relief following social touch in a recipient as part of a feedback loop interaction.

Reputation effects drive the joint evolution of cooperation and social rewarding

People routinely cooperate with each other, even when cooperation is costly. To further encourage such pro-social behaviors, recipients often respond by providing additional incentives, for example by offering rewards. Although such incentives facilitate cooperation, the question remains how these incentivizing behaviors themselves evolve, and whether they would always be used responsibly. Herein, we consider a simple model to systematically study the co-evolution of cooperation and different rewarding policies. In our model, both social and antisocial behaviors can be rewarded, but individuals gain a reputation for how they reward others. By characterizing the game’s equilibria and by simulating evolutionary learning processes, we find that reputation effects systematically favor cooperation and social rewarding. While our baseline model applies to pairwise interactions in well-mixed populations, we obtain similar conclusions under assortment, or when individuals interact in larger groups. According to our model, rewards are most effective when they sway others to cooperate. This view is consistent with empirical observations suggesting that people reward others to ultimately benefit themselves.

Rewards can motivate people to cooperate, but the evolution of rewarding behavior is itself poorly understood. Here, a game-theoretic analysis shows that reputation effects facilitate the simultaneous evolution of cooperation and social rewarding policies.

Holds enable one-shot reciprocal exchange

Strangers routinely cooperate and exchange goods without any knowledge of one another in one-off encounters without recourse to a third party, an interaction that is fundamental to most human societies. However, this act of reciprocal exchange entails the risk of the other agent defecting with both goods. We examine the choreography for safe exchange between strangers, and identify the minimum requirement, which is a shared hold, either of an object, or the other party; we show that competing agents will settle on exchange as a local optimum in the space of payoffs. Truly safe exchanges are rarely seen in practice, even though unsafe exchange could mean that risk-averse agents might avoid such interactions. We show that an 'implicit' hold, whereby an actor believes that they could establish a hold if the other agent looked to be defecting, is sufficient to enable the simple swaps that are the hallmark of human interactions and presumably provide an acceptable trade-off between risk and convenience. We explicitly consider the particular case of purchasing, where money is one of the goods.

Emotional contagion and prosocial behavior in rodents

Empathy is critical to adjusting our behavior to the state of others. The past decade dramatically deepened our understanding of the biological origin of this capacity. We now understand that rodents robustly show emotional contagion for the distress of others via neural structures homologous to those involved in human empathy. Their propensity to approach others in distress strengthens this effect. Although rodents can also learn to favor behaviors that benefit others via structures overlapping with those of emotional contagion, they do so less reliably and more selectively. Together, this suggests evolution selected mechanisms for emotional contagion to prepare animals for dangers by using others as sentinels. Such shared emotions additionally can, under certain circumstances, promote prosocial behavior.

Reaching Out for Inaccessible Food Is a Potential Begging Signal in Cooperating Wild-Type Norway Rats, Rattus norvegicus

Begging is widespread in juvenile animals. It typically induces helpful behaviours in parents and brood care helpers. However, begging is sometimes also shown by adults towards unrelated social partners. Adult Norway rats (Rattus norvegicus) display a sequence of different behaviours in a reciprocal food provisioning task that have been interpreted as such signals of need. The first behaviour in this sequence represents reaching out for a food item the animal cannot obtain independently. This may reflect either an attempt to grasp the food object by itself, or a signal to the social partner communicating the need for help. To distinguish between these two possibilities, we tested in female wild-type Norway rats if the amount of reaching performed by a food-deprived rat changes with the presence/absence of food and a social partner. Focal rats displayed significantly more reaching behaviour, both in terms of number and total duration of events, when food and a potentially helpful partner were present compared to when either was missing. Our findings hence support the hypothesis that rats use reaching behaviour to signal need to social partners that can help them to obtain food.

Dogs fail to reciprocate the receipt of food from a human in a food-giving task

Domestic dogs have been shown to reciprocate help received from conspecifics in food-giving tasks. However, it is not yet known whether dogs also reciprocate help received from humans. Here, we investigated whether dogs reciprocate the receipt of food from humans. In an experience phase, subjects encountered a helpful human who provided them with food by activating a food dispenser, and an unhelpful human who did not provide them with food. Subjects later had the opportunity to return food to each human type, in a test phase, via the same mechanism. In addition, a free interaction session was conducted in which the subject was free to interact with its owner and with whichever human partner it had encountered on that day. Two studies were carried out, which differed in the complexity of the experience phase and the time lag between the experience phase and test phase. Subjects did not reciprocate the receipt of food in either study. Furthermore, no difference was observed in the duration subjects spent in proximity to, or the latency to approach, the two human partners. Although our results suggest that dogs do not reciprocate help received from humans, they also suggest that the dogs did not recognize the cooperative or uncooperative act of the humans during the experience phase. It is plausible that aspects of the experimental design hindered the emergence of any potential reciprocity. However, it is also possible that dogs are simply not prosocial towards humans in food-giving contexts.

Body language signals for rodent social communication

Integration of social cues to initiate adaptive emotional and behavioral responses is a fundamental aspect of animal and human behavior. In humans, social communication includes prominent nonverbal components, such as social touch, gestures and facial expressions. Comparative studies investigating the neural basis of social communication in rodents has historically been centered on olfactory signals and vocalizations, with relatively less focus on non-verbal social cues. Here, we outline two exciting research directions: First, we will review recent observations pointing to a role of social facial expressions in rodents. Second, we will review observations that point to a role of 'non-canonical' rodent body language: body posture signals beyond stereotyped displays in aggressive and sexual behavior. In both sections, we will outline how social neuroscience can build on recent advances in machine learning, robotics and micro-engineering to push these research directions forward towards a holistic systems neurobiology of rodent body language.

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. In a sequential prisoner's dilemma situation, focal subjects encountered four different partners that were either helpful or not, on four consecutive days. On the fifth day, the focal subject was paired with one of the previous four partners and given the opportunity to provide it with food. The focal rats returned received help by closely matching the quantity of help their partner had previously provided, independently of the time delay between received and given help, and independently of the ultimate interaction preceding the test. This shows that direct reciprocity is not limited to dyadic situations in Norway rats, suggesting that cognitive demands involved in applying the required decision rules can be met by non-human animals even when they interact with multiple partners differing in helping propensity.

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 (Rattus norvegicus) 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. When rats were enabled to help a non-cooperative partner while receiving olfactory information from a rat helping a conspecific in a different room, they helped their non-cooperative partner as if it was a cooperative one. We further show that the cues inducing altruistic behaviour are released during the act of cooperation and do not depend on the identity of the cue provider. Remarkably, olfactory cues seem to be more important for cooperation decisions than experiencing a cooperative act per se. This suggests that rats may signal their cooperation propensity to social partners, which increases their chances to receive help in return.

The social life of Norway rats (Rattus norvegicus)

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.

Commodity-specific punishment for experimentally induced defection in cooperatively breeding fish

Coercion is an important but underrated component in the evolution of cooperative behaviour. According to the pay-to-stay hypothesis of cooperative breeding, subordinates trade alloparental care for the concession to stay in the group. Punishment of idle subordinates is a key prediction of this hypothesis, which has received some experimental scrutiny. However, previous studies neither allowed separating between punishment and effects of disruption of social dynamics, nor did they differentiate between different helping behaviours that may reflect either mutualistic or reciprocal interaction dynamics. In the cooperative breeder Neolamprologus pulcher, we experimentally engineered the ability of subordinates to contribute to alloparental care by manipulating two different helping behaviours independently from one another in a full factorial design. We recorded the treatment effects on breeder aggression, subordinate helping efforts and submissive displays. We found two divergent regulatory mechanisms of cooperation, dependent on behavioural function. Experimental impediment of territory maintenance of subordinates triggered punishment by dominants, whereas prevented defence against egg predators released a compensatory response of subordinates without any enforcement, suggesting pre-emptive appeasement. These effects occurred independently of one another. Apparently, in the complex negotiation process among members of cooperative groups, behaviours fulfilling different functions may be regulated by divergent interaction mechanisms.

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. 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 owing 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.

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. Yet, it is unclear how these species reciprocate, given its apparent cognitive complexity. Therefore, our aim was to unravel the psychological processes underlying reciprocity. By bringing together findings from studies investigating different aspects of reciprocity, we show that reciprocity is a rich concept with different behavioural strategies 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 reciprocate. We continue by examining the psychological processes of reciprocity. We show that the cognitive 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.

Do vampire bats groom others based on need?

Allogrooming provides a window into the social lives of many group-living mammals and birds. The fitness benefits of allogrooming are encouraged by proximate mechanisms that make it physiologically rewarding for both actors and receivers. However, receivers might not always benefit from allogrooming. Some allogrooming decisions might be the actor’s response to cues of the recipient’s need. Other decisions might only be caused by the actor’s motivational state. To test these ideas, we studied what triggers allogrooming in common vampire bats. In test 1, subjects that had experimentally disturbed and wetted fur were more likely to be allogroomed, even when controlling for increased self-grooming. In test 2, allogrooming rates were elevated not only by receiver self-grooming (a cue for receiver need) but also by the actor’s previous self-grooming. Both effects were significantly greater than the effect of self-grooming by third parties. Interestingly, we detected a negative interaction: the positive effect of receiver need on allogrooming was smaller when the actor was previously self-grooming. This is consistent with the hypothesis that there are “receiver-driven” allogrooming decisions, which are responses to recipient need, and “actor-driven” decisions, which are not. We predict that receiver-driven allogrooming will bestow greater benefits to recipients compared with actor-driven allogrooming.

Quantitative Matching of Clutch Size in Reciprocating Hermaphroditic Worms

Reciprocity [1] is one of the most controversial evolutionary explanations of cooperation among non-kin [2, 3]. For some authors, cognitive capacity of non-human organisms is limiting, and more parsimonious mechanisms should apply [3-5]; for others, the debate is mainly semantic [2, 6], and empirical evidence can be found in a wide range of taxa [7]. However, while the ability to alternate cooperative behaviors does not settle the reciprocity controversy, the capacity to adjust cooperative behavior to the value of received help could prove decisive. Marine polychaete worms Ophryotrocha diadema, as several simultaneous hermaphrodites, do not self-fertilize and have unilateral mating (i.e., they behave either as females or as males during each mating event). They are also external fertilizers and thus cannot store allosperm, which contribute to make them ideal model organisms to investigate reciprocity, since partners usually alternate sexual roles with each other, repeatedly exchanging egg clutch of variable size [8-12]. However, whether the alternation of sexual roles is the result of conditional reciprocity rather than by-product reciprocity has never been tested [13]. Here, we show that O. diadema worms reciprocate eggs conditionally to the partner's behavior and adjust the quality of cooperation according to that of their partners. Moreover, only egg reciprocation offers similar fitness returns via both the female and the male function with respect to non-reciprocating laying strategies. These results document that fine-tuned forms of conditional reciprocity can emerge in cognitively unsophisticated animals, broadening the criteria to recognize conditional reciprocity among animals.

Comparative Cognition: Rats Pay Back Quid Pro Quo

Humans engage in exchanges of commodities or services, often paying back a commodity with a different service. New research suggests that rats can reciprocally trade food for allogrooming, and vice versa.