Welcome Back: Responses of Female Bonobos (Pan paniscus) to Fusions

Social uncertainty promotes signal complexity during approaches in wild chimpanzees (Pan troglodytes verus) and mangabeys (Cercocebus atys atys)

The social complexity hypothesis for the evolution of communication posits that complex social environments require greater communication complexity for individuals to effectively manage their relationships. We examined how different socially uncertain contexts, reflecting an increased level of social complexity, relate to variation in signalling within and between two species, which display varying levels of fission-fusion dynamics (sympatric-living chimpanzees and sooty mangabeys, Taï National Park, Ivory Coast). Combined signalling may improve message efficacy, notably when involving different perception channels, thus may increase in moments of high social uncertainty. We examined the probability of individuals to emit no signal, single or multisensory or combined (complex) signals, during social approaches which resulted in non-agonistic outcomes. In both species, individuals were more likely to use more combined and multisensory signals in post-conflict approaches with an opponent than in other contexts. The clearest impact of social uncertainty on signalling complexity was observed during chimpanzee fusions, where the likelihood of using complex signals tripled relative to other contexts. Overall, chimpanzees used more multisensory signals than mangabeys. Social uncertainty may shape detected species differences in variation in signalling complexity, thereby supporting the hypothesis that social complexity, particularly associated with high fission-fusion dynamics, promotes signalling complexity.

Bared-teeth displays in bonobos (Pan paniscus): An assessment of the power asymmetry hypothesis

Facial expressions are key to navigating social group life. The Power Asymmetry Hypothesis of Motivational Emancipation predicts that the type of social organization shapes the meaning of communicative displays in relation to an individual's dominance rank. The bared-teeth (BT) display represents one of the most widely observed communicative signals across primate species. Studies in macaques indicate that the BT display in despotic species is often performed unidirectionally, from low- to high-ranking individuals (signaling submission), whereas the BT display in egalitarian species is usually produced irrespective of dominance (mainly signaling affiliation and appeasement). Despite its widespread presence, research connecting BT displays to the power asymmetry hypothesis outside the Macaca genus remains scarce. To extend this knowledge, we investigated the production of BT in relation to social dominance in dyadic interactions (N = 11,377 events) of 11 captive bonobos (Pan paniscus). Although adult bonobos were more despotic than previously suggested in the literature, BT displays were produced irrespective of dominance rank. Moreover, while adults produced the BT exclusively during socio-sexual interactions, especially during periods of social tension, immature bonobos produced the BT in a wider number of contexts. As such, the results indicate that the communicative meaning of the BT display is consistent with signaling appeasement, especially in periods of social tension. Moreover, the BT display does not seem to signal social status, supporting the prediction for species with a high degree of social tolerance. These results advance our understanding of the origins of communicative signals and their relation to species' social systems.

Group Reunion in Zoo European Wildcats Using Cat Appeasing Pheromone (CAP) and Gradual Release of the Animals in the Exhibit—A Case Study

Simple Summary

The present paper is, to our knowledge, the first study that documents the behavioural responses of a group of wildcats kept in a controlled environment upon reunion with one previous member of the social group, a female wildcat, after a long time of separation. The reunion process was gradual, and CAP pheromones were used to minimise agonistic behaviour and to increase the probability of the acceptance of the female. In the first days after the reunion, there was an increase in species-specific behaviours and a reduction in aggressive interactions, but the aggression threshold appeared to lower again after one month, with the behavioural patterns of the late-reunion periods resembling those of the pre-reunion period.

Abstract

The union or reunion of animals with social groups can be a challenging situation, and little has been published about it when solitary species are concerned. Therefore, the aim of the present study was two-fold: (1) to advocate the need for systematic publications about strategies and the outcomes of reunion episodes in zoos and other facilities; and (2) to describe the behaviour of European wildcats (Felis silvestris silvestris) during one such episode, in which a female cat was reintroduced into her family social group using a gradual reunion procedure and cat appeasing pheromone (CAP) (spot-on). The study comprised three periods: the pre-reunion period (10 days, 20 sessions per wildcat), the post-reunion period (A, 5 days, 10 sessions per wildcat; B, 5 days, 10 sessions per wildcat) and the late-reunion period (5 days, 10 sessions per wildcat). In the post-reunion periods, all wildcats were together in the enclosure and were spotted with CAP pheromone. Per period, we collected data on individual and social behaviours. Individual behaviours, such as attention and self-grooming, were performed more in the pre-reunion than in the post-reunion period. Regarding social behaviours, we found that agonistic behaviours were performed more in the pre-reunion than in the post-reunion period. We observed behavioural changes over the course of the study, with behavioural patterns of the late-reunion periods resembling those of the pre-reunion period.

The cooperative sex: Sexual interactions among female bonobos are linked to increases in oxytocin, proximity and coalitions

In some species habitual same-sex sexual behavior co-occurs with high levels of intra-sexual alliance formation, suggesting that these behaviors may be linked. We tested for such a link by comparing behavioral and physiological outcomes of sex with unrelated same- and opposite-sex partners in female bonobos (Pan paniscus). We analyzed behavioral outcomes following 971 sexual events involving n = 19 female and n = 8 male adult and sub-adult members of a wild, habituated bonobo community. We additionally collected n = 143 urine samples before and after sexual interactions to non-invasively measure oxytocin (OT), which modulates female sexual behavior and facilitates cooperation in other species. The majority of sexual events (65%) consisted of female same-sex genito-genital rubbing (or GG-rubbing). Female dyads engaged in significantly more sexual interactions than did inter-sexual dyads, and females were more likely to remain within close proximity to their partners following GG-rubbing. Females also exhibited greater increases in urinary OT following GG-rubbing compared with copulations, indicating a physiological basis for increased motivation to cooperate among females. The frequency of coalitionary support among non-kin was positively predicted by the frequency of sexual interactions for female as well opposite-sex dyads, although coalitionary support tended to be more frequent among females. The emergence of habitual same-sex sexual behavior may have been an important step in the evolution of cooperation outside of kinship and pair-bonds in one of our closest phylogenetic relatives.

Bonobos respond prosocially toward members of other groups

Modern humans live in an "exploded" network with unusually large circles of trust that form due to prosociality toward unfamiliar people (i.e. xenophilia). In a set of experiments we demonstrate that semi-free ranging bonobos (Pan paniscus) - both juveniles and young adults - also show spontaneous responses consistent with xenophilia. Bonobos voluntarily aided an unfamiliar, non-group member in obtaining food even when he/she did not make overt requests for help. Bonobos also showed evidence for involuntary, contagious yawning in response to videos of yawning conspecifics who were complete strangers. These experiments reveal that xenophilia in bonobos can be unselfish, proactive and automatic. They support the first impression hypothesis that suggests xenophilia can evolve through individual selection in social species whenever the benefits of building new bonds outweigh the costs. Xenophilia likely evolved in bonobos as the risk of intergroup aggression dissipated and the benefits of bonding between immigrating members increased. Our findings also mean the human potential for xenophilia is either evolutionarily shared or convergent with bonobos and not unique to our species as previously proposed.

Absence makes the heart grow fonder: social compensation when failure to interact risks weakening a relationship

Social networks require active relationship maintenance if they are to be kept at a constant level of emotional closeness. For primates, including humans, failure to interact leads inexorably to a decline in relationship quality, and a consequent loss of the benefits that derive from individual relationships. As a result, many social species compensate for weakened relationships by investing more heavily in them. Here we study how humans behave in similar situations, using data from mobile call detail records from a European country. For the less frequent contacts between pairs of communicating individuals we observe a logarithmic dependence of the duration of the succeeding call on the time gap with the previous call. We find that such behaviour is likely when the individuals in these dyadic pairs have the same gender and are in the same age bracket as well as being geographically distant. Our results indicate that these pairs deliberately invest more time in communication so as to reinforce their social bonding and prevent their relationships decaying when these are threatened by lack of interaction.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1140/epjds/s13688-016-0097-x) contains supplementary material.

Obstacles and catalysts to peaceful coexistence in chimpanzees and bonobos

As our closest living relatives, comparisons of the social lives and behavioural ecologies of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) provide relevant insights into the evolutionary constraints of peaceful coexistence in Hominid societies. In this review, we compare and contrast findings from the two Pan species in order to examine some of the obstacles and catalysts for peaceful behaviour in our ape relatives. Through comparing the social structures, behavioural mechanisms and ecological drivers for peaceful behaviours in Pan, we develop hypotheses regarding the evolutionary constraints of peaceful co-existence in hominid societies.

Pointing and pantomime in wild apes? Female bonobos use referential and iconic gestures to request genito-genital rubbing

Referential and iconic gesturing provide a means to flexibly and intentionally share information about specific entities, locations, or goals. The extent to which nonhuman primates use such gestures is therefore of special interest for understanding the evolution of human language. Here, we describe novel observations of wild female bonobos (Pan paniscus) using referential and potentially iconic gestures to initiate genito-genital (GG) rubbing, which serves important functions in reducing social tension and facilitating cooperation. We collected data from a habituated community of bonobos at Luikotale, DRC, and analysed n = 138 independent gesture bouts made by n = 11 females. Gestures were coded in real time or from video. In addition to meeting the criteria for intentionality, in form and function these gestures resemble pointing and pantomime–two hallmarks of human communication–in the ways in which they indicated the relevant body part or action involved in the goal of GG rubbing. Moreover, the gestures led to GG rubbing in 83.3% of gesture bouts, which in turn increased tolerance in feeding contexts between the participants. We discuss how biologically relevant contexts in which individuals are motivated to cooperate may facilitate the emergence of language precursors to enhance communication in wild apes.