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Bshary, Redouan

Nom
Bshary, Redouan
Affiliation principale
Fonction
Professeur ordinaire
Email
redouan.bshary@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/343
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0000-0001-7198-8472

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  • Publication
    Accès libre
    Strategic social behaviour in wild vervet monkeys
    (2016)
    Borgeaud, Christèle,
    ;
    Bshary, Redouan 
    In comparison to other vertebrates, primates have a large brain in relation to their body size. It has been hypothesised that the degree of social complexity is the major predictor for such variation. In group living species, individuals face various social challenges which can include finding the right balance between cooperation and competition with other group members. Thus to survive and reproduce individuals would have to show an adapted cognitive flexibility. Following this argument, two parallel hypotheses emerged; the “Machiavellian intelligence” and the “Social brain” hypotheses propose that the social complexity of group living selected respectively for advanced cognitive abilities and an increase in relative brain/neocortex size (i.e. complexity). However, finding a positive correlation between the complexity linked to social life, corresponding advanced cognitive processes and brain size/complexity remains challenging. First, adequate proxies of social complexity that could be applied to various taxa remain to be found. Second, examples of strategic social behaviour such as proposed by the Machiavellian intelligence have been described in many taxa suggesting that more comparative studies are needed to distinguish between advanced cognitive processes and those that could rely on associative learning. Finally, a potential link between cognitive abilities and brain/neocortex size remains largely unexplored.
    By studying wild vervet monkeys (Chlorocebus aethiops) in South Africa, the aim of this thesis was to test for the presence of some social knowledge facets in their behaviour. I also wanted to assess their ability to use such knowledge strategically in both cooperation and competition contexts. Vervet monkeys represent an ideal species as they are highly social, have a strict linear female and male hierarchies and are usually very willing to participate in set-up experiments involving food.
    In Chapter I, I tested the effect of natural migration, births and deaths on the individual centrality and strength of dyadic relationships within the grooming, 1m and 5m proximity social networks (i.e. method 1). I also used a new method (i.e. SIENA; method 2) to test both the network structure and the relationships dynamics. With both methods, I found a strong among-group variation. In addition, results suggest that females and juveniles have more influence than males on the stability at both the individual and dyadic levels, especially within the grooming network. Social relationships might be subject to frequent and significant changes often linked to natural demographic variation. Thus, social network analyses have the potential to capture important aspects of the cognitive social challenges an individual has to cope with. In Chapter II, I conducted rank reversal playbacks to test vervet monkeys’ knowledge about the entire group’s hierarchy. I found that females know about both female and male hierarchies while males and juveniles seem to lack such knowledge about the female hierarchy. Results therefore suggest sex and developmental differences in the extent of third party rank relationships. In Chapter III, I first trained females to consistently approach their personalised boxes to obtain a food reward, which allowed staging potential conflicts by placing two boxes next to each other. With such experiments I could show that subordinates trade grooming for tolerance and coalitionary support and that such trading is modified by the composition of the audience (i.e. individuals within 10m). However data also suggest that subordinates are not able to incorporate the effect of their grooming on dominants’ decision-making to their own advantage.
    In summary, the results of this thesis provide important insights on vervet social strategies and underlying cognitive processes. The introduced methodological advances regarding social network analyses and experimentation to reveal social strategies offer a basis for future research on other primate species for comparison. Such data would then be amenable for correlative studies that link the results to brain evolution. In such a way, one can hope to make important progress regarding the major quest: to assess how social complexity, strategic social behaviours and brain size are interlinked.
  • Publication
    Accès libre
    Social learning and traditions in wild vervet monkeys
    (2010)
    Van de Waal, Erica
    ;
    Bshary, Redouan 
    ;
    Lehmann, Laurent
    ;
    Van Schaik, C.
    Social learning is the basis for allowing the transmission of specific behaviours inside a social unit, i.e. the formation of traditions. Early field studies suggested the existence of traditions in non-human animals, while more recent laboratory experiments have demonstrated social learning abilities in a variety of species. I established a unique bridge between these perspectives by conducting three different social learning experiments on six groups of wild vervet monkeys (Chlorocebus aethiops) at the Loskop Dam Nature Reserve, in South Africa. Using this approach, I investigated what mechanisms wild vervets use when they learn a task socially. Furthermore, theoreticians pointed out that social learning is only driven by positive selection under certain conditions. Therefore, I investigated how important the identity of a model is for the occurrence of social learning and I tried to understand why some individuals are more copied than others from a functional perspective. Finally, by analysing the stability over time of the socially acquired behaviours, I could ask whether traits acquired through social learning may turn into arbitrary traditions. First, I presented laboratory-style ‘artificial fruit’ boxes that had two doors on opposite, differently coloured ends. A dominant individual invariably monopolized the box during an initial demonstration phase, in which one door was blocked. This created consistent demonstrations of one of the two possible solutions in each of six study groups. Three groups had female models and three had male models. Following demonstrations I found a significantly higher participation rate (‘stimulus enhancement’) by other group members and significant evidence for manipulation of the same door (‘local enhancement’) in groups with female models compared to groups with male models. These differences appeared to be due to selective attention of bystanders to female model behaviour, while male and female models attracted similar numbers of bystanders and showed similar levels of aggression towards those bystanders. The results demonstrate the eminent role of dominant females as a source for directed social learning in a species with female philopatry. In this same first experiment, I analysed the proper solving of the task. During their first trial, I observed which individuals managed to open artificial fruit thus accessing the reward. This time I did not find an effect of the model sex but I found that the two groups in contact with humans were more successful than the others. This result suggests some enhanced manipulation skills due to contact with humans or their facilities. The second experiment involved a more complex artificial fruit to test for sequence imitation, where two steps were necessary to open the door: remove a bar on the top of the box which releases a rope that was blocking the door and then pull the door. Vervets largely failed to show more complex social learning abilities in this experimental setup. However monkeys in group with models touched the bar significantly more often during their first manipulation than control individuals did. This latter result implies again the use of ‘local enhancement’ as social learning mechanism in wild vervets. Finally, I conducted a food cleaning experiment that was inspired by a classic study that documented the spread of sweet potato washing in a semi-natural population of Japanese macaques. I offered the monkeys grapes covered with sand and noted if and how they cleaned the food before eating. Each group was subjected to 15 trials. Vervets either did not clean the grapes or either rubbed with their hands, rubbed on substrates, or opened the fruit with their teeth or hands to eat the inside only. I found strong variance between individuals of the same group as well as between groups with respect to the techniques used. Matrilines rather than entire groups appeared to be the key unit for social transmission, where conformity of feeding techniques could be documented. Taken together, the findings imply that in species with complex social structures, migration does not necessarily lead to an exchange of socially acquired information within populations, causing much localized traditions.
  • Publication
    Accès libre
    Selective attention to philopatric models causes directed social learning in wild vervet monkeys
    (2010)
    van de Waal, Erica
    ;
    Renevey, Nathalie
    ;
    Favre, Camille Monique
    ;
    Bshary, Redouan 
    Human behaviour is often based on social learning, a mechanism that has been documented also in a variety of other vertebrates. However, social learning as a means of problem-solving may be optimal only under specific conditions, and both theoretical work and laboratory experiments highlight the importance of a potential model's identity. Here we present the results from a social learning experiment on six wild vervet monkey groups, where models were either a dominant female or a dominant male. We presented ‘artificial fruit’ boxes that had doors on opposite, differently coloured ends for access to food. One option was blocked during the demonstration phase, creating consistent demonstrations of one possible solution. Following demonstrations we found a significantly higher participation rate and same-door manipulation in groups with female models compared to groups with male models. These differences appeared to be owing to selective attention of bystanders to female model behaviour rather than owing to female tolerance. Our results demonstrate the favoured role of dominant females as a source for ‘directed’ social learning in a species with female philopatry. Our findings imply that migration does not necessarily lead to an exchange of socially acquired information within populations, potentially causing highly localized traditions.
  • Publication
    Accès libre
    Differences in Diet Between Six Neighbouring Groups of Vervet Monkeys
    Tournier, Emilie
    ;
    Tournier, Virginia
    ;
    Van de Waal, Erica
    ;
    Barrett, Alan
    ;
    Brown, Leslie
    ;
    Bshary, Redouan 
    The comparative approach provides a powerful tool to study evolutionary questions on both intra- and interspecific variation. It has been applied to a great variety of taxa, including primates. Primate studies differ from those on most other taxa in two ways: first, data from most study sites contain information about only one group. Second, primatologists have used the comparative approach also to identify local traditions, that is, behaviours that spread through social learning. Here, we evaluate the appropriateness of such data by comparing the diet composition of six neighbouring groups of vervet monkeys, Cercopithecus aethiops. We used scan samples to collect diet data, and abundance measures and phenology to assess the availability of the 14 most important tree species utilised during the study. We calculated indices of diet overlap, which were highly variable and could be remarkably low. Furthermore, we found significant differences between group diets with respect to the relative utilisation of 13 of the 14 tree species. For all 13 species, we found positive correlations between local abundance and appearance in the diet, consistent with the importance of local ecology for diet composition. Nevertheless, more detailed comparisons of pairs of groups often revealed significant mismatches between the relative importance of a tree species and its local abundance. In conclusion, local variation merits increased attention by primatologists. While our results are compatible with the possibility that traditions exist on a local (group) rather than population scale, alternative explanations have to be considered.