The Time Frame of Partner Choice in the Grooming Reciprocation ofCebus apella

Emotions and courtship help bonded pairs cooperate, but emotional agents are vulnerable to deceit

Coordinated pair bonds are common in birds and also occur in many other taxa. How do animals solve the social dilemmas they face in coordinating with a partner? We developed an evolutionary model to explore this question, based on observations that a) neuroendocrine feedback provides emotional bookkeeping which is thought to play a key role in vertebrate social bonds and b) these bonds are developed and maintained via courtship interactions that include low-stakes social dilemmas. Using agent-based simulation, we found that emotional bookkeeping and courtship sustained cooperation in the iterated prisoner's dilemma in noisy environments, especially when combined. However, when deceitful defection was possible at low cost, courtship often increased cooperation, whereas emotional bookkeeping decreased it.

Testing the two sides of indirect reciprocity in tufted capuchin monkeys

We addressed two different aspects of indirect reciprocity in tufted capuchin monkeys (Sapajus spp.) studying two common cooperative behaviours, grooming and food sharing. In an observational study, we tested whether capuchin monkeys were more likely to groom an individual that had just groomed a group mate than an individual that had not groomed anybody. In an experimental study, we tested whether capuchin monkeys were more likely to share their food with a partner when in the presence of a bystander (or of an image of the eyes of a conspecific) than when alone with their partner. In the observational study, we found an increase in the likelihood of receiving grooming after giving grooming, but this effect seemed to depend on social facilitation rather than on indirect reciprocity, as we found a similar effect after receiving (rather than giving) grooming. In the experimental study, the presence of a bystander or of an image of eyes did not affect the amount of food transferred to a group mate. Overall, these results suggest capuchin monkeys do not engage in indirect reciprocity.

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.

Time matching between grooming partners: Do methodological distinctions between short versus long-term reciprocation matter?

Primatologists have long focused on grooming exchanges to examine aspects of social relationships, co-operation, and social cognition. One particular interest is the extent to which reciprocating grooming partners time match, and the time frame over which they do so. Conclusions about time matching vary across species. Generally, researchers focus on the duration of pauses between grooming episodes that involve a switch in partner roles and choose a cut-off point to distinguish short from longer-term reciprocation. Problematically, researchers have made inconsistent choices about cut-offs. Such methodological variations are potentially concerning, as it is unclear whether inconsistent conclusions about short-term time matching are attributable to species/ecological differences, or are due in part to methodological inconsistency. We ask whether various criteria for separating short versus long-term reciprocation influence conclusions about short-term time matching using data from free-ranging rhesus ( Macaca mulatta) and captive-crested macaques ( Macaca nigra). We compare several commonly used cut-offs to ones generated by the currently preferred approach-survival analysis. Crested macaques displayed a mild degree of time matching regardless of the cutoff used. For rhesus macaques, whereas most cut-offs yielded similar degrees of time matching as the one derived from survival analysis, very short ones significantly underestimated both the degree of time matching and the influence of rank distance on time matching. Although researchers may have some flexibility in their choice of cut-offs, we suggest that they employ caution by using survival analysis when possible, and when not possible, by avoiding very short time windows.

The dynamics of grooming interactions: maintenance of partner choice and the consequences of demographic variation for female mandrills

A large body of evidence suggests that female Old World monkeys maintain selective long-term grooming interactions with fitness benefits. The last two decades have produced evidence that the regulation of social interactions among primates can be, in part, explained by the Biological Markets theory, with grooming behaviour as the focus of these studies. Grooming facilitates bonding between individuals, constituting an essential part of the regulation of social relationships among female cercopithecids. In contrast to the well-studied baboons (Papio spp), knowledge about the nature of grooming interactions and their regulation is generally lacking for the large, terrestrial species of mandrills (Mandrillus sphinx). We used a combination of social network analysis tools and well-established methods for assessing partner diversity and reciprocity to characterise grooming networks, partner choice and patterns of trade (be groomed, give grooming) among females in a captive group of mandrills, both within and across two separate observation periods. Our results suggest that, even though the relatively stable conditions of captivity allowed the studied females to maintain selective grooming interactions across time, small scale demographic changes affected the grooming dynamics of the group in accordance with the expectations of the Biological Markets theory. In particular, the maturation and consequent integration of a high ranking female into the group's grooming network from one period to the next resulted in a more pronounced effect of rank on the regulation of grooming interactions. In addition, the influence of the maturation of a dependent infant on the grooming interactions of his mother were evident between periods. Our results also demonstrate that grooming networks are dynamic and that high ranking individuals are not necessarily the most central in grooming networks. Finally, we discuss the potential of social network analysis to identify cases of social exclusion and its consequences for captive management.

Rates of human-macaque interactions affect grooming behavior among urban-dwelling rhesus macaques (Macaca mulatta)

OBJECTIVES

The impact of anthropogenic environmental changes may impose strong pressures on the behavioral flexibility of free-ranging animals. Here, we examine whether rates of interactions with humans had both a direct and indirect influence on the duration and distribution of social grooming in commensal rhesus macaques (Macaca mulatta).

MATERIALS AND METHODS

Data were collected in two locations in the city of Shimla in northern India: an urban setting and a temple area. We divided these two locations in a series of similar-sized physical blocks (N = 48) with varying rates of human-macaque interactions. We conducted focal observations on three free-ranging rhesus macaque groups, one in the urban area and two in the temple area.

RESULTS

Our analysis shows that macaques engaged in shorter grooming bouts and were more vigilant while grooming in focal sessions during which they interacted with people more frequently, suggesting that humans directly affected grooming effort and vigilance behavior. Furthermore, we found that in blocks characterized by higher rates of human-macaque interactions grooming bouts were shorter, more frequently interrupted by vigilance behavior, and were less frequently reciprocated.

DISCUSSION

Our work shows that the rates of human-macaque interaction had both a direct and indirect impact on grooming behavior and that macaques flexibly modified their grooming interactions in relation to the rates of human-macaque interaction to which they were exposed. Because grooming has important social and hygienic functions in nonhuman primates, our work suggests that human presence can have important implications for animal health, social relationships and, ultimately, fitness. Our results point to the need of areas away from people even for highly adaptable species where they can engage in social interactions without human disruption.

Cooperation and deception in primates

Though competition and cooperation are often considered opposing forces in an arms race driving natural selection, many animals, including humans, cooperate in order to mitigate competition with others. Understanding others' psychological states, such as seeing and knowing, others' goals and intentions, and coordinating actions are all important for complex cooperation-as well as for predicting behavior in order to take advantage of others through tactical deception, a form of competition. We outline evidence of primates' understanding of how others perceive the world, and then consider how the evidence from both deception and cooperation fits this framework to give us a more complete understanding of the evolution of complex social cognition in primates. In experimental food competitions, primates flexibly manipulate group-mates' behavior to tactically deceive them. Deception can infiltrate cooperative interactions, such as when one takes an unfair share of meat after a coordinated hunt. In order to counter competition of this sort, primates maintain cooperation through partner choice, partner control, and third party punishment. Yet humans appear to stand alone in their ability to understand others' beliefs, which allows us not only to deceive others with the explicit intent to create a false belief, but it also allows us to put ourselves in others' shoes to determine when cheaters need to be punished, even if we are not directly disadvantaged by the cheater.

Correlated pay-offs are key to cooperation

The general belief that cooperation and altruism in social groups result primarily from kin selection has recently been challenged, not least because results from cooperatively breeding insects and vertebrates have shown that groups may be composed mainly of non-relatives. This allows testing predictions of reciprocity theory without the confounding effect of relatedness. Here, we review complementary and alternative evolutionary mechanisms to kin selection theory and provide empirical examples of cooperative behaviour among unrelated individuals in a wide range of taxa. In particular, we focus on the different forms of reciprocity and on their underlying decision rules, asking about evolutionary stability, the conditions selecting for reciprocity and the factors constraining reciprocal cooperation. We find that neither the cognitive requirements of reciprocal cooperation nor the often sequential nature of interactions are insuperable stumbling blocks for the evolution of reciprocity. We argue that simple decision rules such as 'help anyone if helped by someone' should get more attention in future research, because empirical studies show that animals apply such rules, and theoretical models find that they can create stable levels of cooperation under a wide range of conditions. Owing to its simplicity, behaviour based on such a heuristic may in fact be ubiquitous. Finally, we argue that the evolution of exchange and trading of service and commodities among social partners needs greater scientific focus.

Reciprocity in group-living animals: partner control versus partner choice

Reciprocity is probably the most debated of the evolutionary explanations for cooperation. Part of the confusion surrounding this debate stems from a failure to note that two different processes can result in reciprocity: partner control and partner choice. We suggest that the common observation that group-living animals direct their cooperative behaviours preferentially to those individuals from which they receive most cooperation is to be interpreted as the result of the sum of the two separate processes of partner control and partner choice. We review evidence that partner choice is the prevalent process in primates and propose explanations for this pattern. We make predictions that highlight the need for studies that separate the effects of partner control and partner choice in a broader variety of group-living taxa.

"Targeting or supporting, what drives patterns of aggressive intervention in fights?"

GrooFiWorld is an individual-based, computational model of social interactions that can be used to examine factors underlying reciprocation and interchange of social behavior in primate societies. Individuals within GrooFiWorld are programed to maintain spatial proximity and thereby form a group. When an individual encounters another individual in its proximity, the individual attacks the other if the risk of losing is low. Otherwise, the individual considers grooming the other. Patterns of social behavior that emerge in the model resemble empirical data from primates. Triadic aggression emerges when an individual attacks one of the former combatants by chance immediately after an aggressive interaction, and reciprocation and interchange of grooming and support emerge even though individuals have no intention to help others or pay back services. The model generates predictions for patterns of contra-intervention that are counterintuitive within a framework of interchange of social services, such as that individuals receive more contra-intervention from those whom they groom more frequently. Here we tested these predictions in data collected on social interactions in a group of bonnet macaques (Macaca radiata). We confirmed the predictions of the model in the sense that contra-intervention was strongly correlated with dyadic aggression which suggests that contra-intervention is a subset of dyadic aggression. Adult females directed more contra-intervention to those individuals from whom they received more grooming. Further, contra-intervention was directed down the dominance hierarchy such that adult females received more contra-intervention from higher ranking females. Because these findings are consistent with the predictions from the GrooFiWorld model, they suggest that the distribution of interventions in fights is regulated by factors such as dominance rank and spatial structure rather than a motivation to help others and interchange social services.

Egalitarian despots: hierarchy steepness, reciprocity and the grooming-trade model in wild chimpanzees, Pan troglodytes

Biological market theory models the action of natural selection as a marketplace in which animals are viewed as traders with commodities to offer and exchange. Studies of female Old World monkeys have suggested that grooming might be employed as a commodity to be reciprocated or traded for alternative services, yet previous tests of this grooming-trade model in wild adult male chimpanzees have yielded mixed results. Here we provide the strongest test of the model to date for male chimpanzees: we use data drawn from two social groups (communities) of chimpanzees from different populations and give explicit consideration to variation in dominance hierarchy steepness, as such variation results in differing conditions for biological markets. First, analysis of data from published accounts of other chimpanzee communities, together with our own data, showed that hierarchy steepness varied considerably within and across communities and that the number of adult males in a community aged 20-30 years predicted hierarchy steepness. The two communities in which we tested predictions of the grooming-trade model lay at opposite extremes of this distribution. Second, in accord with the grooming-trade model, we found evidence that male chimpanzees trade grooming for agonistic support where hierarchies are steep (despotic) and consequent effective support is a rank-related commodity, but not where hierarchies are shallow (egalitarian). However, we also found that grooming was reciprocated regardless of hierarchy steepness. Our findings also hint at the possibility of agonistic competition, or at least exclusion, in relation to grooming opportunities compromising the free market envisioned by biological market theory. Our results build on previous findings across chimpanzee communities to emphasize the importance of reciprocal grooming exchanges among adult male chimpanzees, which can be understood in a biological markets framework if grooming by or with particular individuals is a valuable commodity.

Food transfers in capuchin monkeys: an experiment on partner choice

Although most primates live in groups, experiments on reciprocity usually test individuals in dyads. This could hide the processes emerging in richer social settings, reducing the ecological validity of the results. We run an experiment on reciprocal food transfers testing capuchin monkeys (Cebus apella) in triads, so that subjects could choose to allow access to their food to either of their two partners. We tested the hypothesis that partner choice was related to a comparison of long-term social bonds with the two partners, more than to a comparison of recent food transfer events from the two partners. The results confirmed this hypothesis, thus supporting the notion that reciprocal partner preferences are based on long-term accounts of benefits that have been exchanged.

Are monkeys able to plan for future exchange?

Whether or not non-human animals can plan for the future is a hotly debated issue. We investigate this question further and use a planning-to-exchange task to study future planning in the cooperative domain in two species of monkeys: the brown capuchin (Cebus apella) and the Tonkean macaque (Macaca tonkeana). The rationale required subjects to plan for a future opportunity to exchange tokens for food by collecting tokens several minutes in advance. Subjects who successfully planned for the exchange task were expected to select suitable tokens during a collection period (5/10 min), save them for a fixed period of time (20/30 min), then take them into an adjacent compartment and exchange them for food with an experimenter. Monkeys mostly failed to transport tokens when entering the testing compartment; hence, they do not seem able to plan for a future exchange with a human partner. Three subjects did however manage to solve the task several times, albeit at very low rates. They brought the correct version of three possible token types, but rarely transported more than one suitable token at a time. Given that the frequency of token manipulation predicted transport, success might have occurred by chance. This was not the case, however, since in most cases subjects were not already holding the token in their hands before they entered the testing compartment. Instead, these results may reflect subjects' strengths and weaknesses in their time-related comprehension of the task.

Male Mating Tactics in Captive Rhesus Macaques (Macaca mulatta): The Influence of Dominance, Markets, and Relationship Quality

Male mating success in a multimale-multifemale group can depend on several variables: body condition, dominance, coalitions, "friendship," or an exchange of services for mating access. Exchange patterns may also be determined by market effects or social relationships. We studied the mating tactics of males in a captive, multimale-multifemale group of rhesus macaques and the resulting patterns of mating and paternity to determine the influence of dominance rank, mating markets, and relationship quality on their mating tactics. Male rank was positively related to the total number of copulations and the number of mating partners, but did not explain male mating distribution completely. Moreover, male fertilization success was not related to male rank. Males did not exchange grooming for mating access on the same day and neither the supply nor the rank (as a proxy for quality) of receptive females affected the amount of male grooming, suggesting that market effects did not explain male mating access. However, there was a positive correlation between long-term grooming patterns of both males and females and mating access, indicating that social relationships were important for male mating access. Paternity data revealed that these social relationships were also important for male reproductive success. We conclude that both male rank and male-female "friendship" determined male mating access in these rhesus macaques, but that "friendship" was more important in determining paternity, emphasizing the importance of intersex social bonds in male mating success in multimale primate societies. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s10764-011-9552-5) contains supplementary material, which is available to authorized users.

Reciprocation and interchange of grooming, agonistic support, feeding tolerance, and aggression in semi-free-ranging Barbary macaques

Evidence from a range of primate species indicates that grooming can be exchanged either for itself or for other rank-related "commodities," such as agonistic support, feeding tolerance, or reduced aggression. Patterns of exchange behavior have been found to vary considerably between species, and understanding the causes of this variation is central to the study of the evolution of primate social systems. It is, therefore, essential that exchange behavior is examined in a wide range of species and settings. This article is the first to explore the reciprocation and interchange of grooming in the Barbary macaque (Macaca sylvanus). We collected focal data on semi-free-ranging adult female Barbary macaques at Trentham Monkey Forest, England, and analyzed dyadic data using Generalized Linear Mixed Models. We found evidence for the reciprocal exchange of grooming and for the interchange of grooming for agonistic support and tolerance while feeding. There was no evidence that grooming was traded for a reduction in aggression; indeed, we found a positive relationship between aggression given and grooming received. This may reflect the "extortion" of grooming from subordinates by dominant animals. These results will facilitate comparative analyses of exchange behavior by adding to the current database a new species, characterized by a different social style from those macaque species previously investigated.

Resolving the iterated prisoner's dilemma: theory and reality

Pairs of unrelated individuals face a prisoner's dilemma if cooperation is the best mutual outcome, but each player does best to defect regardless of his partner's behaviour. Although mutual defection is the only evolutionarily stable strategy in one-shot games, cooperative solutions based on reciprocity can emerge in iterated games. Among the most prominent theoretical solutions are the so-called bookkeeping strategies, such as tit-for-tat, where individuals copy their partner's behaviour in the previous round. However, the lack of empirical data conforming to predicted strategies has prompted the suggestion that the iterated prisoner's dilemma (IPD) is neither a useful nor realistic basis for investigating cooperation. Here, we discuss several recent studies where authors have used the IPD framework to interpret their data. We evaluate the validity of their approach and highlight the diversity of proposed solutions. Strategies based on precise accounting are relatively uncommon, perhaps because the full set of assumptions of the IPD model are rarely satisfied. Instead, animals use a diverse array of strategies that apparently promote cooperation, despite the temptation to cheat. These include both positive and negative reciprocity, as well as long-term mutual investments based on 'friendships'. Although there are various gaps in these studies that remain to be filled, we argue that in most cases, individuals could theoretically benefit from cheating and that cooperation cannot therefore be explained with the concept of positive pseudo-reciprocity. We suggest that by incorporating empirical data into the theoretical framework, we may gain fundamental new insights into the evolution of mutual reciprocal investment in nature.

Group size, grooming and fission in primates: a modeling approach based on group structure

In social animals, fission is a common mode of group proliferation and dispersion and may be affected by genetic or other social factors. Sociality implies preserving relationships between group members. An increase in group size and/or in competition for food within the group can result in decrease certain social interactions between members, and the group may split irreversibly as a consequence. One individual may try to maintain bonds with a maximum of group members in order to keep group cohesion, i.e. proximity and stable relationships. However, this strategy needs time and time is often limited. In addition, previous studies have shown that whatever the group size, an individual interacts only with certain grooming partners. There, we develop a computational model to assess how dynamics of group cohesion are related to group size and to the structure of grooming relationships. Groups' sizes after simulated fission are compared to observed sizes of 40 groups of primates. Results showed that the relationship between grooming time and group size is dependent on how each individual attributes grooming time to its social partners, i.e. grooming a few number of preferred partners or grooming equally or not all partners. The number of partners seemed to be more important for the group cohesion than the grooming time itself. This structural constraint has important consequences on group sociality, as it gives the possibility of competition for grooming partners, attraction for high-ranking individuals as found in primates' groups. It could, however, also have implications when considering the cognitive capacities of primates.

A few misunderstandings about reciprocal altruism

Current discussion about reciprocal altruism is plagued by a few points of continuing disagreement/misunderstanding. In order to facilitate progress in understanding the role of reciprocity in animal societies, in this paper we try to highlight these points of disagreement/misunderstanding. Our contribution can be summarized by the following statements: (1) A temporal contingency between action and reciprocation is not the sole valid evidence for reciprocal altruism; (2) Reciprocity is not (always) cognitively demanding; (3) Kin biases in altruism are not necessarily and entirely due to kin selection; (4) Mutualism can also involve reciprocal partner choice; (5) Biological market theory is an extension of reciprocal altruism theory.

The relative roles of kinship and reciprocity in explaining primate altruism

Several hypotheses have been proposed to explain the evolution of altruistic behaviours. Their relative roles in explaining actual cases of animal altruism are, however, unclear. In particular, while kin selection is widely believed to have a pervasive influence on animal behaviour, reciprocity is generally thought to be rare. Despite this general agreement, there has been no direct test comparing the relative roles of kinship and reciprocity in explaining animal altruism. In this paper, we report on the results of such a test based on a meta-analysis of allogrooming in primates, grooming being probably the most common altruistic behaviour among mammals. In direct contrast to the prevailing view, reciprocity played a much larger role than kinship in explaining primate allogrooming. These results point to a more significant role of reciprocity in the evolution of animal altruism than is generally acknowledged.