Recipients affect prosocial and altruistic choices in jackdaws, Corvus monedula

Family first! Influence of parental investment in Guinea pigs (Cavia porcellus) prosocial choices

Literature often assumed that prosocial behaviours (behaviours that benefit others with or without a cost for the actor) would have evolved many species to improve the effectiveness of parental care (Decety and Cowell 2014). While this hypothesis is rarely questioned at a phylogenetic scale, it was never tested at an individual scale to the best of our knowledge. Therefore, we chose to study the impact of effective parental care on prosociality by comparing the prosocial tendencies of Guinea pigs before mating, during mating and after parturition. We conducted Prosocial Choice Tests on three groups of Guinea pigs (males, multiparous females, and nulliparous females). Subjects had to choose between three options: a prosocial option (subject and recipient being rewarded), a selfish option (only subject was rewarded), and a null option (no reward). Our results showed high prosociality towards their mating partner and their young both in male and in female subjects. Males became selfish towards other males after parturition. Among other interesting results, we found a direct reciprocity phenomenon. We also highlighted an ability in our subjects to consider both the identity and relationship shared with the recipient, such as tolerance (enhancing prosociality), dominance rank (being tested with a dominant recipient increasing selfish responses), and its behaviour (begging calls eliciting prosociality, while threatening ones decreasing it), to choose an option. These findings suggested that prosociality could be modulated by many factors and that the constraints and stakes induced by breeding would highly influence prosocial strategies.

Third-party intervention and post-conflict behaviour in agonistic encounters of pigs (Sus scrofa)

BACKGROUND

Third-party interference in agonistic contests entails a deliberate intervention in an ongoing fight by a bystanding individual (third party) and may be followed by post-conflict social behaviour to provide support to a specific individual. The mechanisms behind third-party intervention are, however, still largely understudied. The aim of this study was to investigate third-party interference, with the predictions that (1) the interferer derives benefits from its action by winning a fight, (2) that patterns of intervention depend on familiarity, (3) that dyadic fights last longer than triadic fights, and (4) that interferers engage in non-agonistic social behaviours afterwards. Pre-pubertal pigs (Sus scrofa) (n = 384) were grouped with one familiar and four unfamiliar conspecifics (all non-kin) to elicit contests for dominance rank. Third-party interference was analysed for the first 30 min after grouping, along with the behaviour (nosing or aggression), contest duration, contest outcome, and interferer behaviour after the fight (post-conflict social behaviour).

RESULTS

Three types of interference were observed: non-agonistic involvement (nose contact) by the interferer in a dyadic fight; a triadic fight with each of three contestants fighting one opponent at a time; and triadic fights with two opponents jointly attacking the third one (two-against-one fights). The likelihood of a third-party intervention to occur did not depend on the presence of a familiar animal in the fight. However, once intervention was triggered, interferers attacked unfamiliar fight initiators more than familiar ones. Two-against-one fights lasted longer than other triadic fights and occurred more often when both initial contestants were females. Results of 110 triadic fights (out of 585 fights in total) revealed that interferers were more likely to win compared to the initial opponents at equal body weight. The most common post-conflict behaviour displayed by the interferer was agonistic behaviour towards another group member, independently of familiarity.

CONCLUSIONS

The general lack of discrimination for familiarity suggests interference is not driven by support to familiar individuals in pigs. The results show that intervening in an ongoing fight gives the interferer a high chance of contest success and may be a strategy that is beneficial to the interferer to increase its dominance status.

Prosociality and reciprocity according to parental status, communication, and personality in domestic canaries (Serinus canaria)

Prosociality (behaviours that benefit to a recipient without necessarily involving a cost to the actor) has recently been shown to exist in various taxa, including birds. Studies on prosociality in primates found that prosocial tendencies of the subject could be related to sex and parental care, communication from the recipient, cognitive abilities and personality. To investigate the existence of such associations on birds, we conducted a Prosocial Choice Task with domestic canaries (Serinus canaria). In our experiment, the subject could choose between three options: a prosocial, a selfish, and a null option (with no cost for the subject). We also conducted a food sharing experiment and measured several personality traits. Our results highlighted high levels of prosociality and a tendency to reciprocity among reproductive mates. We found a higher propensity to be prosocial in nulliparous individuals than in individuals that have previously been parents, but better sharing abilities in parents than in nulliparous individuals. When they were recipient, parents also used communication more efficiently than nulliparous subjects. Data suggest that parental expertise could enhance subjects' skills in eliciting prosociality. We also highlighted some interaction between prosociality, learning abilities, and some personality traits, proactive individuals being fast learners and more prosocial, while reactive individuals being slow learners and more reciprocal. Our results suggest that prosociality and reciprocity could be linked to personality and cognitive abilities, and that it might be interesting to consider them as parts of individual's cognitive style.

Multimodal cues displayed by submissive rats promote prosocial choices by dominants

Animals often display prosocial behaviors, performing actions that benefit others. Although prosociality is essential for social bonding and cooperation, we still know little about how animals integrate behavioral cues from those in need to make decisions that increase their well-being. To address this question, we used a two-choice task where rats can provide rewards to a conspecific in the absence of self-benefit and investigated which conditions promote prosociality by manipulating the social context of the interacting animals. Although sex or degree of familiarity did not affect prosocial choices in rats, social hierarchy revealed to be a potent modulator, with dominant decision-makers showing faster emergence and higher levels of prosocial choices toward their submissive cage mates. Leveraging quantitative analysis of multimodal social dynamics prior to choice, we identified that pairs with dominant decision-makers exhibited more proximal interactions. Interestingly, these closer interactions were driven by submissive animals that modulated their position and movement following their dominants and whose 50-kHz vocalization rate correlated with dominants' prosociality. Moreover, Granger causality revealed stronger bidirectional influences in pairs with dominant focals and submissive recipients, indicating increased behavioral coordination. Finally, multivariate analysis highlighted body language as the main information dominants use on a trial-by-trial basis to learn that their actions have effects on others. Our results provide a refined understanding of the behavioral dynamics that rats use for action-selection upon perception of socially relevant cues and navigate social decision-making.

Mate Choice, Sex Roles and Sexual Cognition in Vertebrates: Mate Choice Turns Cognition or Cognition Turns Mate Choice?

The idea of “smart is sexy,” meaning superior cognition provides competitive benefits in mate choice and, therefore, evolutionary advantages in terms of reproductive fitness, is both exciting and captivating. Cognitively flexible individuals perceive and adapt more dynamically to (unpredictable) environmental changes. The sex roles that females and males adopt within their populations can vary greatly in response to the prevalent mating system. Based on how cognition determines these grossly divergent sex roles, different selection pressures could possibly shape the (progressive) evolution of cognitive abilities, suggesting the potential to induce sexual dimorphisms in superior cognitive abilities. Associations between an individual’s mating success, sexual traits and its cognitive abilities have been found consistently across vertebrate species and taxa, providing evidence that sexual selection may well shape the supporting cognitive prerequisites. Yet, while superior cognitive abilities provide benefits such as higher feeding success, improved antipredator behavior, or more favorable mate choice, they also claim costs such as higher energy levels and metabolic rates, which in turn may reduce fecundity, growth, or immune response. There is compelling evidence in a variety of vertebrate taxa that females appear to prefer skilled problem-solver males, i.e., they prefer those that appear to have better cognitive abilities. Consequently, cognition is also likely to have substantial effects on sexual selection processes. How the choosing sex assesses the cognitive abilities of potential mates has not been explored conclusively yet. Do cognitive skills guide an individual’s mate choice and does learning change an individual’s mate choice decisions? How and to which extent do individuals use their own cognitive skills to assess those of their conspecifics when choosing a mate? How does an individual’s role within a mating system influence the choice of the choosing sex in this context? Drawing on several examples from the vertebrate world, this review aims to elucidate various aspects associated with cognitive sex differences, the different roles of males and females in social and sexual interactions, and the potential influence of cognition on mate choice decisions. Finally, future perspectives aim to identify ways to answer the central question of how the triad of sex, cognition, and mate choice interacts.

Individual Goffin´s cockatoos (Cacatua goffiniana) show flexible targeted helping in a tool transfer task

Flexible targeted helping is considered an advanced form of prosocial behavior in hominoids, as it requires the actor to assess different situations that a conspecific may be in, and to subsequently flexibly satisfy different needs of that partner depending on the nature of those situations. So far, apart from humans such behaviour has only been experimentally shown in chimpanzees and in Eurasian jays. Recent studies highlight the prosocial tendencies of several bird species, yet flexible targeted helping remained untested, largely due to methodological issues as such tasks are generally designed around tool-use, and very few bird species are capable of tool-use. Here, we tested Goffin's cockatoos, which proved to be skilled tool innovators in captivity, in a tool transfer task in which an actor had access to four different objects/tools and a partner to one of two different apparatuses that each required one of these tools to retrieve a reward. As expected from this species, we recorded playful object transfers across all conditions. Yet, importantly and similar to apes, three out of eight birds transferred the correct tool more often in the test condition than in a condition that also featured an apparatus but no partner. Furthermore, one of these birds transferred that correct tool first more often before transferring any other object in the test condition than in the no-partner condition, while the other two cockatoos were marginally non-significantly more likely to do so. Additionally, there was no difference in the likelihood of the correct tool being transferred first for either of the two apparatuses, suggesting that these birds flexibly adjusted what to transfer based on their partner´s need. Future studies should focus on explanations for the intra-specific variation of this behaviour, and should test other parrots and other large-brained birds to see how this can be generalized across the class and to investigate the evolutionary history of this trait.

Carrion Crows and Azure-Winged Magpies Show No Prosocial Tendencies When Tested in a Token Transfer Paradigm

To study the evolution of humans' cooperative nature, researchers have recently sought comparisons with other species. Studies investigating corvids, for example, showed that carrion crows and azure-winged magpies delivered food to group members when tested in naturalistic or simple experimental paradigms. Here, we investigated whether we could replicate these positive findings when testing the same two species in a token transfer paradigm. After training the birds to exchange tokens with an experimenter for food rewards, we tested whether they would also transfer tokens to other birds, when they did not have the opportunity to exchange the tokens themselves. To control for the effects of motivation, and of social or stimulus enhancement, we tested each individual in three additional control conditions. We witnessed very few attempts and/or successful token transfers, and those few instances did not occur more frequently in the test condition than in the controls, which would suggest that the birds lack prosocial tendencies. Alternatively, we propose that this absence of prosociality may stem from the artificial nature and cognitive complexity of the token transfer task. Consequently, our findings highlight the strong impact of methodology on animals' capability to exhibit prosocial tendencies and stress the importance of comparing multiple experimental paradigms.

No preference for prosocial helping behavior in rats with concurrent social interaction opportunities

Helping behavior tasks are proposed to assess prosocial or "empathic" behavior in rodents. This paradigm characterizes the behavior of subject animals presented with the opportunity to release a conspecific from a distressing situation. Previous studies found a preference in rats for releasing restrained or distressed conspecifics over other controls (e.g., empty restrainers or inanimate objects). An empathy account was offered to explain the observed behaviors, claiming subjects were motivated to reduce the distress of others based on a rodent homologue of empathy. An opposing account attributes all previous results to subjects seeking social contact. To dissociate these two accounts for helping behavior, we presented subject rats with three simultaneous choice alternatives: releasing a restrained conspecific, engaging a nonrestrained conspecific, or not socializing. Subjects showed an initial preference for socializing with the nonrestrained conspecific, and no preference for helping. This result contradicts the empathy account, but is consistent with the social-contact account of helping behavior.

Prosocial and antisocial choices in a monogamous cichlid with biparental care

Human society is cooperative and characterized by spontaneous prosociality. Comparative studies on endotherm vertebrates suggest that social interdependence causes the evolution of proactive prosociality. To test the generality of this hypothesis, we modify a prosocial choice task for application to the convict cichlid, Amatitlania nigrofasciata, a monogamous fish with biparental care and a strong pair bond. We also affirm that male subjects learn to favor prosocial choices when their mates are the recipients in a neighboring tank. When the neighboring tank is empty, males choose randomly. Furthermore, in the absence of their mates, males behave prosocially toward a stranger female. However, if the mate of the subjects is also visible in the third tank, or if a male is a potential recipient, then subjects make antisocial choices. To conclude, fish may show both spontaneous prosocial and antisocial behaviors according to their social relationships with conspecifics and the overall social context.

Targeted helping and cooperation in zoo-living chimpanzees and bonobos

Directly comparing the prosocial behaviour of our two closest living relatives, bonobos and chimpanzees, is essential to deepening our understanding of the evolution of human prosociality. We examined whether helpers of six dyads of chimpanzees and bonobos transferred tools to a conspecific. In the experiment 'Helping', transferring a tool did not benefit the helper, while in the experiment 'Cooperation', the helper only obtained a reward by transferring the correct tool. Chimpanzees did not share tools with conspecifics in either experiment, except for a mother-daughter pair, where the mother shared a tool twice in the experiment 'Helping'. By contrast, all female-female bonobo dyads sometimes transferred a tool even without benefit. When helpers received an incentive, we found consistent transfers in all female-female bonobo dyads but none in male-female dyads. Even though reaching by the bonobo receivers increased the likelihood that a transfer occurred, we found no significant species difference in whether receivers reached to obtain tools. Thus, receivers' behaviour did not explain the lack of transfers from chimpanzee helpers. This study supports the notion that bonobos might have a greater ability to understand social problems and the collaborative nature of such tasks.

Sex-specific effects of cooperative breeding and colonial nesting on prosociality in corvids

The investigation of prosocial behavior is of particular interest from an evolutionary perspective. Comparisons of prosociality across non-human animal species have, however, so far largely focused on primates, and their interpretation is hampered by the diversity of paradigms and procedures used. Here, we present the first systematic comparison of prosocial behavior across multiple species in a taxonomic group outside the primate order, namely the bird family Corvidae. We measured prosociality in eight corvid species, which vary in the expression of cooperative breeding and colonial nesting. We show that cooperative breeding is positively associated with prosocial behavior across species. Also, colonial nesting is associated with a stronger propensity for prosocial behavior, but only in males. The combined results of our study strongly suggest that both cooperative breeding and colonial nesting, which may both rely on heightened social tolerance at the nest, are likely evolutionary pathways to prosocial behavior in corvids.

Pro-social preference in an automated operant two-choice reward task under different housing conditions: Exploratory studies on pro-social decision making

In this study, we aimed to develop a behavioral task that measures pro-social decision making in rats. A fully automated, operant pro-social two-choice task is introduced that quantifies pro-social preferences for a mutual food reward in a set-up with tightly controlled task contingencies. Pairs of same-sex adult Wistar rats were placed in an operant chamber divided into two compartments (one rat per compartment), separated by a transparent barrier with holes that allowed the rats to see, hear, smell, but not touch each other. Test rats could earn a sucrose pellet either for themselves (own reward) or for themselves and the partner (both reward) by means of lever pressing. On average, male rats showed a 60 % preference for the lever that yielded a food reward for both themselves and their partner. In contrast, females did not show lever preference, regardless of the estrous cycle phase. Next, the impact of juvenile environmental factors on male rat social decision making was studied. Males were group-housed from postnatal day 26 onwards in complex housing Marlau™ cages that provided social and physical enrichment and stimulation in the form of novelty. Complex housed males did not show a preference for the pro-social lever.

Parrots Voluntarily Help Each Other to Obtain Food Rewards

Helping others to obtain benefits, even at a cost to oneself, poses an evolutionary puzzle [1]. While kin selection explains such "selfless" acts among relatives, only reciprocity (paying back received favors) entails fitness benefits for unrelated individuals [2]. So far, experimental evidence for both prosocial helping (providing voluntary assistance for achieving an action-based goal) and reciprocity has been reported in a few mammals but no avian species [3]. In order to gain insights into the evolutionary origins of these behaviors, the capacity of non-mammalian species for prosociality and for reciprocity needs to be investigated. We tested two parrot species in an instrumental-helping paradigm involving "token transfer." Here, actors could provide tokens to their neighbor, who could exchange them with an experimenter for food. To verify whether the parrots understood the task's contingencies, we systematically varied the presence of a partner and the possibility for exchange. We found that African grey parrots voluntarily and spontaneously transferred tokens to conspecific partners, whereas significantly fewer transfers occurred in the control conditions. Transfers were affected by the strength of the dyads' affiliation and partially by the receivers' attention-getting behaviors. Furthermore, the birds reciprocated the help once the roles were reversed. Blue-headed macaws, in contrast, transferred hardly any tokens. Species differences in social tolerance might explain this discrepancy. These findings show that instrumental helping based on a prosocial attitude, accompanied but potentially not sustained by reciprocity, is present in parrots, suggesting that this capacity evolved convergently in this avian group and mammals.

Not by the same token: A female orangutan (Pongo pygmaeus) is selectively prosocial

Studies of prosocial behavior in nonhumans have focused on group-living social animals. Despite being highly social and closely related to humans, chimpanzees have rarely exhibited prosocial preferences in experimental tasks. Fewer studies have provided their non group-living relatives-orangutans-with the opportunity to express prosocial preferences. Here, we allowed a single female orangutan to provide rewards for herself and for her mother, sister, or both, across various phases, using a token economy task. The orangutan was more likely to choose prosocially when she could provide rewards to her sister and herself compared to when she could provide rewards to her mother and herself. However, when presented with the simultaneous options of providing rewards for self, self and mother, or self and sister, she chose prosocially equally often to her mother and sister. She made the largest number of prosocial choices in a phase when she could provide rewards to all participants (herself, her sister, and her mother) rather than providing rewards only to herself or only to herself and one other participant. Despite the obvious limitations of a single case study, the study adds to the limited information on prosocial preferences in less social primate species, particularly when given the chance to share food items with different kin.

Assessing African grey parrots' prosocial tendencies in a token choice paradigm

Prosociality is defined as a voluntary, typically low-cost behaviour that benefits another individual. Social tolerance has been proposed as a potential driver for its evolution, both on the proximate and on the ultimate level. Parrots are an interesting species to study such other-regarding behaviours, given that they are highly social and stand out in terms of relative brain size and cognitive capacity. We tested eight African grey parrots in a dyadic prosocial choice test. They faced a choice between two different tokens, a prosocial (actor and partner rewarded) and a selfish (only actor rewarded) one. We found that the birds did not behave prosocially when one subject remained in the actor role; however, when roles were alternated, the birds' prosocial choices increased. The birds also seemed to reciprocate their partner's choices, given that a contingency between choices was observed. If the food provisioned to the partner was of higher quality than that the actor obtained, actors increased their willingness to provide food to their partner. Nonetheless, the control conditions suggest that the parrots did not fully understand the task's contingencies. In sum, African grey parrots show the potential for prosociality and reciprocity; however, considering their lack of understanding of the contingencies of the particular tasks used in this study, the underlying motivation for the observed behaviour remains to be addressed by future studies, in order to elucidate the phylogenetic distribution of prosociality further.

Mesotocin influences pinyon jay prosociality

Many species exhibit prosocial behaviour, in which one individual's actions benefit another individual, often without an immediate benefit to itself. The neuropeptide oxytocin is an important hormonal mechanism influencing prosociality in mammals, but it is unclear whether the avian homologue mesotocin plays a similar functional role in birds. Here, we experimentally tested prosociality in pinyon jays (Gymnorhinus cyanocephalus), a highly social corvid species that spontaneously shares food with others. First, we measured prosocial preferences in a prosocial choice task with two different pay-off distributions: Prosocial trials delivered food to both the subject and either an empty cage or a partner bird, whereas Altruism trials delivered food only to an empty cage or a partner bird (none to subject). In a second experiment, we examined whether administering mesotocin influenced prosocial preferences. Compared to choices in a control condition, we show that subjects voluntarily delivered food rewards to partners, but only when also receiving food for themselves (Prosocial trials), and administration of high levels of mesotocin increased these behaviours. Thus, in birds, mesotocin seems to play a similar functional role in facilitating prosocial behaviours as oxytocin does in mammals, suggesting an evolutionarily conserved hormonal mechanism for prosociality.

Proactive prosociality in a cooperatively breeding corvid, the azure-winged magpie (Cyanopica cyana)

One of the contemporary hypotheses concerning the evolution of human altruism is the cooperative breeding hypothesis (CBH) which has recently been tested in non-human primates. Using a similar paradigm, we investigated prosociality in a cooperatively breeding corvid, the azure-winged magpie. We found that the magpies delivered food to their group members at high rates, and unlike other corvids, they did so without any cues provided by others. In two control conditions, the magpies stopped participating over time, indicating that they learned to discriminate prosocial tests from controls. Azure-winged magpies are thus the first birds that experimentally show proactive prosociality. Our findings are in line with the CBH; however, additional corvid species need to be tested in this promising paradigm.

Meerkats (Suricata suricatta) fail to prosocially donate food in an experimental set-up

Although humans are usually believed to be prosocial, the evolutionary origins of prosociality are largely debated. One hypothesis is that cooperative breeding has been one major precursor to the emergence of prosociality. In vertebrates, however, experimental evidence of prosociality has been mainly gathered in non-human primates. In this study, we tested the cooperative breeding hypothesis in cooperative breeding meerkats (Suricata suricatta). In particular, we tested whether meerkats take into account partners' benefits when distributing food rewards. Nine individuals were presented with two platforms baited with different food distributions (providing food to themselves, to a partner or both). In all conditions, the decision to operate the apparatus was based on the presence of food on the subject's side, and not on the possible benefits to partners. Despite being cooperative breeders, meerkats in this study failed to be prosocial, suggesting that prosociality in this species may be limited to specific contexts.

Distinct selective forces and Neanderthal introgression shaped genetic diversity at genes involved in neurodevelopmental disorders

In addition to high intelligence, humans evolved specialized social-cognitive skills, which are specifically affected in children with autism spectrum disorder (ASD). Genes affected in ASD represent suitable candidates to study the evolution of human social cognition. We performed an evolutionary analysis on 68 genes associated to neurodevelopmental disorders; our data indicate that genetic diversity was shaped by distinct selective forces, including natural selection and introgression from archaic hominins. We discuss the possibility that segregation distortion during spermatogenesis accounts for a subset of ASD mutations. Finally, we detected modern-human-specific alleles in DYRK1A and TCF4. These variants are located within regions that display chromatin features typical of transcriptional enhancers in several brain areas, strongly suggesting a regulatory role. These SNPs thus represent candidates for association with neurodevelopmental disorders, and await experimental validation in future studies.

Clark's Nutcrackers (Nucifraga columbiana) Flexibly Adapt Caching Behavior to a Cooperative Context

Corvids recognize when their caches are at risk of being stolen by others and have developed strategies to protect these caches from pilferage. For instance, Clark's nutcrackers will suppress the number of caches they make if being observed by a potential thief. However, cache protection has most often been studied using competitive contexts, so it is unclear whether corvids can adjust their caching in beneficial ways to accommodate non-competitive situations. Therefore, we examined whether Clark's nutcrackers, a non-social corvid, would flexibly adapt their caching behaviors to a cooperative context. To do so, birds were given a caching task during which caches made by one individual were reciprocally exchanged for the caches of a partner bird over repeated trials. In this scenario, if caching behaviors can be flexibly deployed, then the birds should recognize the cooperative nature of the task and maintain or increase caching levels over time. However, if cache protection strategies are applied independent of social context and simply in response to cache theft, then cache suppression should occur. In the current experiment, we found that the birds maintained caching throughout the experiment. We report that males increased caching in response to a manipulation in which caches were artificially added, suggesting the birds could adapt to the cooperative nature of the task. Additionally, we show that caching decisions were not solely due to motivational factors, instead showing an additional influence attributed to the behavior of the partner bird.

Dogs Do Not Show Pro-social Preferences towards Humans

Pro-social behaviors are defined as voluntary actions that benefit others. Comparative studies have mostly focused on investigating the presence of pro-sociality across species in an intraspecific context. Taken together, results on both primates and non-primate species indicate that reliance on cooperation may be at work in the selection and maintenance of pro-social sentiments. Dogs appear to be the ideal model when investigating a species’ propensity for pro-sociality in an interspecific context because it has been suggested that as a consequence of domestication, they evolved an underlying temperament encouraging greater propensity to cooperate with human partners. In a recent study, using a food delivery paradigm, dogs were shown to preferentially express pro-social choices toward familiar compared to unfamiliar conspecifics. Using the same set-up and methods in the current study, we investigated dogs’ pro-social preferences toward familiar and unfamiliar human partners. We found that dogs’ pro-social tendencies did not extend to humans and the identity of the human partners did not influence the rate of food delivery. Interestingly, dogs tested with their human partners spent more time gazing at humans, and did so for longer after food consumption had ended than dogs tested with conspecific partners in the initial study. To allow comparability between results from dogs tested with a conspecific and a human partner, the latter were asked not to communicate with dogs in any way. However, this lack of communication from the human may have been aversive to dogs, leading them to cease performing the task earlier compared to the dogs paired with familiar conspecifics in the prior study. This is in line with previous findings suggesting that human communication in such contexts highly affects dogs’ responses. Consequently, we encourage further studies to examine dogs’ pro-social behavior toward humans taking into consideration their potential responses both with and without human communication.

Critical issues in experimental studies of prosociality in non-human species

Prosociality and acts of altruism are defined as behaviours which benefit another with either no gain or some immediate cost to the self. To understand the evolutionary origins of these behaviours, in recent years, studies have extended to primate species; however, studies on non-primates are still scarce. In light of the fact that phylogenetic closeness to humans does not appear to correlate with prosocial tendencies, but rather differences in the propensity towards prosociality may be linked to allomaternal care or collaborative foraging, it appears that convergent selection pressures may be at work in the evolution of prosociality. It would hence seem particularly important to extend such studies to species outside the primate clade, to allow for comparative hypothesis testing of the factors affecting the evolution of prosocial behaviours. In the current review, we focus on the experimental paradigms which have been used so far (i.e. the prosocial choice task, helping paradigms and food-sharing tests) and highlight the strengths and weaknesses of each method. In line with the aim of encouraging a broader comparative approach to the topic of prosociality, particular emphasis is placed on the methodological issues that need to be taken into account. We conclude that although a number of the paradigms used so far may be successfully applied to non-primate species, there is a need to simplify the cognitive demands of the tasks and ensure task comprehension to allow for a 'fair' comparative approach of prosocial tendencies across species.

Familiarity affects other-regarding preferences in pet dogs

Other-regarding preferences are considered to be the foundation of human cooperation. However, the evolutionary origin of this behavior in humans remains poorly understood. So far, comparative studies in primates have led to mixed conclusions probably due to methodological differences relating to both task complexity and the types of control conditions used. Moreover, no clear link between phylogenetic relatedness and prosociality has been found, suggesting that other convergent selection pressures may play a role in the evolution of such behaviors. Here, using one of the cognitively less demanding tasks, we show for the first time, that dogs can behave pro-socially by donating food to a conspecific partner, but only if the partner is familiar. This highlights the importance of considering the social relationships between individuals when testing animals for other-regarding behaviors. Moreover, by including a social control condition, we show that the dogs’ prosocial response was not due to a simple social facilitation effect. The current findings support recent proposals that other convergent selection pressures, such as dependence on cooperative activities, rather than genetic relatedness to humans, may shape a species’ propensity for other-regarding behaviors.

Cooperation in wild Barbary macaques: factors affecting free partner choice

A key aspect of cooperation is partner choice: choosing the best available partner improves the chances of a successful cooperative interaction and decreases the likelihood of being exploited. However, in studies on cooperation subjects are rarely allowed to freely choose their partners. Group-living animals live in a complex social environment where they can choose among several social partners differing in, for example, sex, age, temperament, or dominance status. Our study investigated whether wild Barbary macaques succeed to cooperate using an experimental apparatus, and whether individual and social factors affect their choice of partners and the degree of cooperation. We used the string pulling task that requires two monkeys to manipulate simultaneously a rope in order to receive a food reward. The monkeys were free to interact with the apparatus or not and to choose their partner. The results showed that Barbary macaques are able to pair up with a partner to cooperate using the apparatus. High level of tolerance between monkeys was necessary for the initiation of successful cooperation, while strong social bond positively affected the maintenance of cooperative interactions. Dominance status, sex, age, and temperament of the subjects also affected their choice and performance. These factors thus need to be taken into account in cooperative experiment on animals. Tolerance between social partners is likely to be a prerequisite for the evolution of cooperation.

Subadult ravens generally don't transfer valuable tokens to conspecifics when there is nothing to gain for themselves

The extent to which humans help each other is extraordinary in itself, and difficult to explain from an evolutionary perspective. Therefore, there has been a recent surge in studies investigating the evolution of prosocial behavior using a comparative approach. Nevertheless, most of these studies have focused on primates only, and little is known about other animal orders. In a previous study, common ravens (Corvus corax) have been shown to be indifferent to the gains of conspecifics. However, this may have been due to the experimental set-up, as many studies that use different set-ups report conflicting results within the same species. We therefore tested ravens' prosocial tendencies in a different set-up; i.e., we tested whether sub-adult ravens would transfer a token to a partner and, thereby, provide the partner with the opportunity to exchange a token for a reward. To control and test for effects of partner identity, we tested eight individuals both in a dyadic and in a group setting. Our results show that in general the ravens in our experiment did not show other-regarding preferences. However, some acts of helping did occur spontaneously. We discuss what could be the causes for those sporadic instances, and why in general prosocial tendencies were found to be almost lacking among the ravens in this set-up.

Prosocial Choice in Rats Depends on Food-Seeking Behavior Displayed by Recipients

Animals often are prosocial, displaying behaviors that result in a benefit to one another [1-15] even in the absence of self-benefit [16-21] (but see [22-25]). Several factors have been proposed to modulate these behaviors, namely familiarity [6, 13, 18, 20] or display of seeking behavior [16, 21]. Rats have been recently shown to be prosocial under distress [17, 18] (but see [26-29]); however, what drives prosociality in these animals remains unclear. To address this issue, we developed a two-choice task in which prosocial behavior did not yield a benefit or a cost to the focal rat. We used a double T-maze in which only the focal rat controlled access to the food-baited arms of its own and the recipient rat's maze. In this task, the focal rat could choose between one side of the maze, which yielded food only to itself (selfish choice), and the opposite side, which yielded food to itself and the recipient rat (prosocial choice). Rats showed a high proportion of prosocial choices. By manipulating reward delivery to the recipient and its ability to display a preference for the baited arm, we found that the display of food-seeking behavior leading to reward was necessary to drive prosocial choices. In addition, we found that there was more social investigation between rats in selfish trials than in prosocial trials, which may have influenced the focals' choices. This study shows that rats provide access to food to others in the absence of added direct self-benefit, bringing new insights into the factors that drive prosociality.

Empathy: gender effects in brain and behavior

Evidence suggests that there are differences in the capacity for empathy between males and females. However, how deep do these differences go? Stereotypically, females are portrayed as more nurturing and empathetic, while males are portrayed as less emotional and more cognitive. Some authors suggest that observed gender differences might be largely due to cultural expectations about gender roles. However, empathy has both evolutionary and developmental precursors, and can be studied using implicit measures, aspects that can help elucidate the respective roles of culture and biology. This article reviews evidence from ethology, social psychology, economics, and neuroscience to show that there are fundamental differences in implicit measures of empathy, with parallels in development and evolution. Studies in nonhuman animals and younger human populations (infants/children) offer converging evidence that sex differences in empathy have phylogenetic and ontogenetic roots in biology and are not merely cultural byproducts driven by socialization. We review how these differences may have arisen in response to males' and females' different roles throughout evolution. Examinations of the neurobiological underpinnings of empathy reveal important quantitative gender differences in the basic networks involved in affective and cognitive forms of empathy, as well as a qualitative divergence between the sexes in how emotional information is integrated to support decision making processes. Finally, the study of gender differences in empathy can be improved by designing studies with greater statistical power and considering variables implicit in gender (e.g., sexual preference, prenatal hormone exposure). These improvements may also help uncover the nature of neurodevelopmental and psychiatric disorders in which one sex is more vulnerable to compromised social competence associated with impaired empathy.

Human-Grey parrot (Psittacus erithacus) reciprocity: a follow-up study

In a previous study (Péron et al. in Anim Cogn, doi: 10.1007/s10071-012.05640 , 2012), Grey parrots, working in dyads, took turns choosing one of four differently coloured cups with differing outcomes: empty (null, non-rewarding), selfish (keeping reward for oneself), share (sharing a divisible reward), or giving (donating reward to other). When the dyads involved three humans with different specific intentions (selfish, giving, or copying the bird's behaviour), birds' responses only tended towards consistency with human behaviour. Our dominant bird was willing to share a reward with a human who was willing to give up her reward, was selfish with the selfish human, and tended towards sharing with the copycat human; our subordinate bird tended slightly towards increased sharing with the generous human and selfishness with the selfish human, but did not clearly mirror the behaviour of the copycat. We theorized that the birds' inability to understand the copycat condition fully-that they could potentially maximize reward by choosing to share-was a consequence of their viewing the copycat's behaviour as erratic compared with the consistently selfish or giving humans and thus not realizing that they were indeed being mirrored. We suggested that copycat trials subsequently be performed as a separate experiment, without being contrasted with trials in which humans acted consistently, in order to determine if results might have differed. We have now performed that experiment, and shown that at least one Grey parrot--our dominant--responded in a manner suggesting that he deduced the appropriate contingencies.

Capuchins' (Cebus apella) sensitivity to others' goal-directed actions in a helping context

As humans, our ability to help others effectively is at least in part dependent upon our capacity to infer others' goals in a variety of different contexts. Several species of nonhuman primate have demonstrated that they will also help others in some relatively simple situations, but it is not always clear whether this helping is based on an understanding of another agent's goals. Although the results of a number of different studies support the hypothesis that chimpanzees represent others' goals in various helping contexts and are sensitive to these goals when actually helping others, less work has addressed whether more distantly related species actively represent goals when helping. To explore the cognitive mechanisms underlying helping behaviors in species less closely related to humans, we tested whether a species of New World monkey-the brown capuchin (Cebus apella)-would provide an experimenter with a desired out-of-reach object more often than an alternative object when the experimenter attempted to obtain the former object only. We found that capuchins reliably helped by providing the experimenter's goal object (Experiment 1) and that explanations based on the use of several less sophisticated strategies did not account for the overall pattern of data (Experiments 2-4). Results are thus consistent with the hypothesis that capuchins help others based on an understanding of their goals although more work is needed to address the possibility that capuchins may be responding to gestural and postural factors alone.

Hand rearing affects emotional responses but not basic cognitive performance in European starlings

Hand rearing is a common procedure in behavioural research on birds. While likely to produce tamer experimental animals, there is a risk that it could induce pathological changes in brain and behaviour similar to those seen in mammals that have experienced maternal separation. We explored the effects of hand rearing on the cognitive and behavioural development of European starlings, Sturnus vulgaris, to assess the generality of results obtained from hand-reared animals. Two groups of age-matched birds were created from the same wild population: one hand-reared from 10 days posthatch and one brought into the laboratory as independent juveniles. These groups were compared on a battery of neuropsychological tasks designed to probe different aspects of cognitive function including learning, perseverative cognition, interval timing, neophobia and impulsivity. There was no evidence for cognitive impairment in the hand-reared birds. They did not have reduced learning speed, impairments in accuracy or precision of interval timing or pathological perseverative cognition compared to the wild-caught birds. Additionally, there was no evidence that birds that developed stereotypies in laboratory cages (predominantly the wild-caught birds) had any cognitive impairments, although this may be because no birds had severe, crystallized stereotypies. There was some evidence that hand-reared birds were less neophobic and less impulsive than wild-caught birds, suggesting that hand rearing might alter emotionally mediated decision making in a direction usually associated with reduced developmental stress in mammals. This study therefore supports the use of hand rearing as an experimental procedure in behavioural research on passerine birds.

Ravens (Corvus corax) are indifferent to the gains of conspecific recipients or human partners in experimental tasks

Although cooperative behaviours are common in animals, the cognitive processes underpinning such behaviours are very likely to differ between species. In humans, other-regarding preferences have been proposed to sustain long-term cooperation between individuals. The extent to which such psychological capacities exist in other animals is still under investigation. Five hand-reared ravens were first tested in an experiment where they could provide food to a conspecific at no cost to themselves. We offered them two behavioural options that provided identical amounts of food to the actor and where one of the two options additionally delivered a reward to a recipient. Subsequently, we made the ravens play a no-cost cooperation game with an experimenter. The experimenter had the same options as the animals and matched the ravens' choices, making the prosocial choice the more profitable option. In both conditions, ravens were indifferent to the effects of their choices and hence failed to help conspecifics and to cooperate with the experimenter. While our negative results should be interpreted with care, overall, our findings suggest that the ravens had no understanding of the consequences of their actions for a potential recipient. This study adds to several others that have used a similar set-up and have reported negative results on other-regarding preferences in animals.