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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
_
0000-0001-7198-8472

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  • Publication
    Accès libre
    Social-learning abilities of wild vervet monkeys in a two-step task artificial fruit experiment
    (2011)
    van de Waal, Erica
    ;
    Bshary, Redouan 
    Social learning is the basis for the formation of traditions in both human and nonhuman animals. Field observations and experiments provide evidence for the existence of traditions in animals but they do not address the underlying social-learning mechanisms. We used an established laboratory experimental paradigm, the artificial fruit design, to test for copying of a sequence of actions and local enhancement in six groups of wild vervet monkeys, Chlorocebus aethiops. We introduced a two-step task where models had to remove a bar to untie a rope that blocked a single door of a box. The models were high-ranking individuals that monopolized the box early on and discovered by trial and error how to open it. We obtained successful models in three groups, while the other three groups acted as controls. After 20 successful demonstrations, we tested subjects with a box that had a rope in the same position but the rope was not functional. Under these conditions, sequential copying of the two-step opening did not occur. Only individuals that were exposed to models were likely to touch the bar if door opening was not immediately successful, providing evidence for local enhancement. When we presented the boxes with the functional rope, we found no effect of having been exposed to a model on the probability that subjects solved the task. We conclude that the social-learning abilities of wild vervet monkeys are relatively limited and discuss potential problems concerning the technical difficulty of the task.
  • 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
    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
    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.