Fake or not: Two prerequisites for jealousy

Cook and colleagues (2018) use a novel approach to test jealousy in dogs. Although such a non-invasive approach is more than welcome in comparative research, several methodological shortcomings limit the impact of this study. We briefly outline two main problems. (1) There is no evidence that the fake dogs in the study were perceived as real, and thus as social rivals, which would be a prerequisite for jealousy. (2) It is questionable whether dogs generally show the cognitive prerequisites for jealousy, such as attentiveness toward a social rival, the ability to understand intentions, and a sense of fairness. We suggest that future studies should combine the same creativity with more controlled procedures in order to better understand the evolutionary origins of jealousy

There is no Other Monkey in the Mirror for Spider Monkeys (Ateles geoffroyi)

©American Psychological Association, 2020. This paper is not the copy of record and may not exactly replicate the authoritative document published in the APA journal. Please do not copy or cite without author's permission. The final article is available, upon publication, at: https://doi.org/10.1037/com0000243Mirror self-recognition (MSR), usually considered a marker of self-awareness, occurs in several species and may reflect a capacity that has evolved in small incremental steps. In line with research on human development and building on previous research adopting a gradualist framework, we categorized the initial mirror responses of naïve spider monkeys (Ateles geoffroyi) according to four levels. We compared social, exploratory, contingent and self-exploratory responses to a mirror and faux mirror during three short trials. If spider monkeys respond as most monkey species, we predicted they would perform at level 0, mainly showing social behavior toward their mirror-image. However, because spider monkeys show enhancement of certain cognitive skills comparable to those of great ape species, we predicted that they would perform at level 1a (showing exploratory behavior) or 1b (showing contingent behavior). GLMMs revealed that monkeys looked behind and visually inspected the mirror significantly more in the mirror than the faux mirror condition. Although the monkeys engaged in contingent body movements at the mirror, this trend was not significant. Strikingly, they showed no social behaviors toward their mirror-image. We also measured self-scratching as an indicator of anxiety and found no differences in frequencies of self-scratching between conditions. Therefore, in contrast to most findings on other species, spider monkeys did not treat their image as another monkey during their initial exposure to the mirror. In fact, they reached at least level 1a within minutes of mirror exposure. These responses recommend spider monkeys as good candidates for further explorations into monkey self-recognition

Innovation in wild Barbary macaques (Macaca sylvanus)

Innovation is the ability to solve novel problems or find novel solutions to familiar problems, and it is known to affect fitness in both human and non-human animals. In primates, innovation has been mostly studied in captivity, although differences in living conditions may affect individuals’ ability to innovate. Here, we tested innovation in a wild group of Barbary macaques (Macaca sylvanus). In four different conditions, we presented the group with several identical foraging boxes containing food. To understand which individual characteristics and behavioural strategies best predicted innovation rate, we measured the identity of the individuals manipulating the boxes and retrieving the food, and their behaviour during the task. Our results showed that success in the novel task was mainly affected by the experimental contingencies and the behavioural strategies used during the task. Individuals were more successful in the 1-step conditions, if they participated in more trials, showed little latency to approach the boxes and mainly manipulated functional parts of the box. In contrast, we found no effect of inhibition, social facilitation and individual characteristics like sex, age, rank, centrality, neophobia and reaction to humans, on the individuals’ ability to innovate

Lack of prosociality in great apes, capuchin monkeys and spider monkeys : convergent evidence from two different food distribution tasks

This work was conducted while the first author held a Humboldt Research Fellowship for Postdoctoral Researchers (Humboldt ID no. 1138999).Prosociality can be defined as any behaviour performed to alleviate the needs of others or to improve their welfare. Prosociality has probably played an essential role in the evolution of cooperative behaviour and several studies have already investigated it in primates to understand the evolutionary origins of human prosociality. Two main tasks have been used to test prosociality in a food context. In the Platforms task, subjects can prosocially provide food to a partner by selecting a prosocial platform over a selfish one. In the Tokens task, subjects can prosocially provide food to a partner by selecting a prosocial token over a selfish one. As these tasks have provided mixed results, we used both tasks to test prosociality in great apes, capuchin monkeys and spider monkeys. Our results provided no compelling evidence of prosociality in a food context in any of the species tested. Additionally, our study revealed serious limitations of the Tokens task as it has been previously used. These results highlight the importance of controlling for confounding variables and of using multiple tasks to address inconsistencies present in the literature.PostprintPeer reviewe

Intra-specific variation in the social behaviour of Barbary macaques (Macaca sylvanus)

Non-human primates show an impressive behavioural diversity, both across and within species. However, the factors explaining intra-specific behavioural variation across groups and individuals are yet understudied. Here, we aimed to assess how group size and living conditions (i.e. captive, semi-free-ranging, wild) are linked to behavioural variation in 5 groups of Barbary macaques (N=137 individuals). In each group, we collected observational data on the time individuals spent in social interactions and on the group dominance style, along with experimental data on social tolerance over food and neophobia. Our results showed that differences in group size predicted differences in the time spent in social interactions, with smaller groups spending a higher proportion of time in close spatial proximity, but a lower proportion of time grooming. Moreover, group size predicted variation in dominance style, with smaller groups being more despotic. Social tolerance was affected by both group size and living conditions, being higher in smaller groups and in groups living in less natural conditions. Finally, individual characteristics also explained variation in social tolerance and neophobia, with socially integrated individuals having higher access to food sources, and higher-ranking ones being more neophobic. Overall, our results support the view that intra-specific variation is a crucial aspect in primate social behaviour, and call for more comparative studies to better understand the sources of within-species variation

Gaze Following in Ungulates: Domesticated and Non-domesticated Species Follow the Gaze of Both Humans and Conspecifics in an Experimental Context

Gaze following is the ability to use others' gaze to obtain information about the environment (e.g., food location, predators, and social interactions). As such, it may be highly adaptive in a variety of socio-ecological contexts, and thus be widespread across animal taxa. To date, gaze following has been mostly studied in primates, and partially in birds, but little is known on the gaze following abilities of other taxa and, especially, on the evolutionary pressures that led to their emergence. In this study, we used an experimental approach to test gaze following skills in a still understudied taxon, ungulates. Across four species (i.e., domestic goats and lamas, and non-domestic guanacos and mouflons), we assessed the individual ability to spontaneously follow the gaze of both conspecifics and human experimenters in different conditions. In line with our predictions, species followed the model's gaze both with human and conspecific models, but more likely with the latter. Except for guanacos, all species showed gaze following significantly more in the experimental conditions (than in the control ones). Despite the relative low number of study subjects, our study provides the first experimental evidence of gaze following skills in non-domesticated ungulates, and contributes to understanding how gaze following skills are distributed in another taxon-an essential endeavor to identify the evolutionary pressures leading to the emergence of gaze following skills across taxa