From the first intention movement to the last joiner: macaques combine mimetic rules to optimize their collective decisions.

Mechanisms related to collective decision making have recently been found in almost all animal reigns from amoebae to worms, insects and vertebrates, including human beings. Decision-making mechanisms related to collective movements-including pre-departure and joining-have already been studied at different steps of the movement process, but these studies were always carried out separately. We therefore have no understanding of how these different processes are related when they underlie the same collective decision-making event. Here, we consider the whole departure process of two groups of Tonkean macaques (Macaca tonkeana), using a stochastic model. When several exclusive choices are proposed, macaques vote and choose the majority. Individuals then join the movement according to a mimetism based on affiliative relationships. The pre-departure quorum and the joining mimetic mechanism are probably linked, but we have not yet identified which transition mechanism is used. This study shows that decision-making related to macaque group movements is governed by a quorum rule combined with a selective mimetism at departure. This is the first time that transition mechanisms have been described in mammals, which consequently helps understand how a voting process leads to social amplification. Our study also provides the first complete proof that there is continuity in the decision-making processes underlying collective movements in mammals from the first intention movement right through to the last joiner.

Short-term group fission processes in macaques: a social networking approach.

Living in groups necessarily involves a certain amount of within-group competition for food. Group members may have different motivations, implying the reaching of a consensus to stay cohesive. In some cases individuals fail to reach a common decision and the group splits; this can be temporary, as seen in fission-fusion dynamics, or even irreversible. Most studies on fission-fusion dynamics published to date have focused on the influence of environmental constraints on sub-grouping patterns, but little is known about how social relationships affect individual choices for sub-groups. In this study, we used an agent-based model to understand the mechanisms underlying group fission in two semi-free-ranging groups of macaques: one group of Tonkean macaques (Macaca tonkeana) and one of rhesus macaques (M. mulatta). The results showed that sub-grouping patterns were mainly influenced by affiliative relationships. Moreover, the species-specific social style appeared to affect the probability of choosing a particular sub-group. In the tolerant Tonkean macaques, mechanisms underlying sub-grouping patterns resembled anonymous mimetism, while in the nepotistic rhesus macaques, kinship influenced the mechanisms underlying group fissions. As previous studies have shown, fission-fusion society may be a way to avoid social conflicts induced either by food or by social competition.

Collective decision-making in white-faced capuchin monkeys.

In group-living animals, collective movements are a widespread phenomenon and occur through consensus decision. When one animal proposes a direction for group movement, the others decide to follow or not and hence take part in the decision-making process. This paper examines the temporal spread of individual responses after the departure of a first individual (the initiator) in a semi-free ranging group of white-faced capuchins (Cebus capucinus). We analysed 294 start attempts, 111 succeeding and 183 failing. Using a modelling approach, we have demonstrated that consensus decision-making for group movements is based on two complementary phenomena in this species: firstly, the joining together of group members thanks to a mimetic process; and secondly, a modulation of this phenomenon through the propensity of the initiator to give up (i.e. cancellation rate). This cancellation rate seems to be directly dependent upon the number of followers: the greater this number is, the lower the cancellation rate is seen to be. The coupling between joining and cancellation rates leads to a quorum: when three individuals join the initiator, the group collectively moves. If the initiator abandons the movement, this influences the joining behaviour of the other group members, which in return influences the initiator's behaviour. This study demonstrates the synergy between the initiator's behaviour and the self-organized mechanisms underlying group movements.

The influence of social organisation on leadership in brown lemurs (Eulemur fulvus fulvus) in a controlled environment.

Studies on leadership during group movements in several lemur species showed that females were responsible for the travelling choices concerning time and direction. Interestingly, in these species females are dominant over males. We investigated the influence of social organisation upon leadership processes by studying a lemur species in which social organisation is characterized by the absence of female dominance: the brown lemur (Eulemur fulvus fulvus). The study was conducted on a semi-free ranging group of 11 individuals and the analysis performed on 69 group movements showed that all the individuals could initiate a group movement. In 34 cases, the whole group moved. There was no significant difference in the number of start attempts or in the number of group members involved from one initiator to another. Moreover, there was no effect of sex or age of the initiator on the number of individuals following it or on the speed of the joining process. Therefore, the leadership observed is widely distributed to all group members. These results support the hypothesis of an influence of social organisation upon the decision-making processes but still remain to be studied in a more relevant ecological context.

Social play in crested and Japanese macaques: testing the covariation hypothesis.

Most studies about social play have focused on its function in aiding socialization. It is not known whether play patterns vary by species according to specific adult social relationships. To test whether there is covariation between the form of play interactions and adult relationships, we studied social play in Japanese macaques (Macaca fuscata) and crested macaques (Macaca nigra). Comparative studies have shown that whereas low levels of tolerance and strict hierarchies characterize Japanese macaques, crested macaques display greater tolerance and relaxed dominance. The results showed that the former prefer less risky games, with minimal physical contact, ease of escape and a small number of play partners. The play bouts of the latter species involve closer contact and more partners. We conclude that play patterns covary with specific social style. Play patterns could have been selected for to introduce youngsters to their future social environment.

Shared or unshared consensus decision in macaques?

Members of a social group have to make collective decisions in order to synchronise their activities. In a shared consensus decision, all group members can take part in the decision whereas in an unshared consensus decision, one individual, usually a dominant member of the group, takes the decision for the rest of the group. It has been suggested that the type of decision-making of a species could be influenced by its social style. To investigate this further, we studied collective movements in two species with opposed social systems, the Tonkean macaque (Macaca tonkeana) and the rhesus macaque (Macaca mulatta). From our results, it appears that the decision to move is the result of the choices and actions of several individuals in both groups. However, this consensus decision involved nearly all group members in Tonkean macaques whereas dominant and old individuals took a prominent role in rhesus macaques. Thus, we suggest that Tonkean macaques display equally shared consensus decisions to move, whereas in the same context rhesus macaque exhibit partially shared consensus decisions. Such a difference in making a collective decision might be linked to the different social systems of the two studied species.

Resource influence on the form of fur rubbing behaviour in white-faced capuchins.

Self-medicative behaviours have been largely documented in vertebrates and, in particular, the use of plants for pharmacological purposes has been mainly reported in primates. White-faced capuchins are known to rub specifically chosen plants and other substances on their fur. To better understand the mechanisms underlying this phenomenon and investigate the influence of different plant resources on the form of fur rubbing activity, we conducted experiments using different randomly selected plant items: oranges and onions. We found that (1) capuchins showed different degrees of interest in the materials used to fur rub; (2) the mean group dynamics differ drastically according to the resource supplied; and (3) individuals present strong differences in their social behaviour, i.e. they spent more or less time fur rubbing in spatial proximity of conspecifics according to the material used for fur rubbing. We propose hypotheses on possible proximal causes for these differences and highlight that some precautions have to be taken in behavioural studies including only one resource type.

Social facilitation of fur rubbing behavior in white-faced capuchins.

In their natural environment, capuchins select certain plants, containing secondary compounds with bactericide, insecticide or fungicide properties, to rub their pelage energetically (i.e. fur rubbing). Fur rubbing can be performed in solitary, or collectively in subgroups of variable size and composition, and most of the time fur rubbing happens in synchrony with other group members. The aim of this study is to understand the underlying mechanisms of this phenomenon, and, more particularly, to determine the processes involved in its synchronization. For this purpose, we designed a set of experiments where white-faced capuchins (Cebus capucinus) were presented with onions (Allium cepa) that they use to fur rub. We conducted a detailed kinetic study of fur rubbing behavior to determine if its synchronization is the consequence of simultaneous responses of different individuals to the same stimulus or if, on the contrary, there is a real collective phenomenon where individuals respond to conspecific behavior. Our results reveal that fur rubbing is a collective behavior with a mimetic underlying mechanism. If fur rubbing with onions (a plant with antifungal and repellent properties) allows capuchins to treat their fur against parasites or pathogens, its synchronization would optimize the treatment by acting as a group barrier to ectoparasite propagation.

[Factor impact and indexing in bibliographic databases: comparison of these quality criteria for the assessment of pharmaceutical journals]. / Facteur d'impact et indexation dans les bases de données bibliographiques: comparaison de ces deux critères de qualité pour l'évaluation des revues pharmaceutiques.

In spite of limits, the impact factor (IF) of Journal Citation Reports (JCR) of Science Citation Index (SCI) edited by the Institute for Scientific Information (ISI) is the most currently used bibliometric factor by scientists. Otherwise, bibliographic systems select and index scientific journals with their own quality criterion. In order to bring scientists and information professionals some new journal evaluation developments, we studied and compared pharmaceutical journal IF and the number of bibliographic systems in which they were indexed. We firstly have given our definition of pharmaceutical journal and then evaluated these journals by giving one point each time they were indexed in one of the five following bibliographic systems: Index Medicus/Medline, Excerpta Medica/Embase, International Pharmaceutical Abstracts, Chemical Abstracts, Current Contents. We then compared their results with IF. We selected 292 journals: 14.4% scored 5 points, 22.3% scored 4 points, 27.7% scored 3 points, 18.8% scored 2 points, 16.8% scored 1 point. We also showed that the more journals scored highly, the more they had chances of being taken by JCR. We studied the first hundred journals indexed by JCR and having the highly IF: 31, 40, 21, 6 and 2 journals were respectively indexed by 5, 4, 3, 2 and 1 bibliographic systems. We showed that there was a significant difference between the two classifications. So, we can say that people who take IF as the one and only journal quality criterion have in fact a very partial representation of the edition of scientific papers.