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.     

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.     

How can leadership processes in European bison be used to improve the management of free-roaming herds

For several years, several wild species are experiencing a comeback in Europe, especially large herbivores. Despite the good news, the increased number of wild herbivores also potentially increases human-wildlife conflicts due to crop damages and road traffic accidents where such species have been involved in previously. In this context, studying the movements of animal groups is particularly relevant for managing their use of space and ensure sufficient cohabitation with human populations. We thus studied the European bison (Bison bonasus), a species concerned in several rewilding programs, to understand to what extent individual characteristics and social relationships are involved in the leadership process and how these factors influence the success of group movements. We observed a herd of 14 individuals in Zuid-Kennemerland National Park (the Netherlands) and analysed the initiation phase of spontaneous group movements. We showed that leadership was distributed throughout the group but the two oldest females showed higher propensity to initiate and to be followed. They seemed to have a high social power and a strong capacity to federate probably due to their dominance rank and their knowledge of the areas. The joining process was faster when animals were grouped before departure and when the initiator moved in the direction towards which the majority of individuals was oriented. Individuals joined the movement according to a selective mimetic process, based on kinship. These results, combined with virtual fence device, could be used to manage herd movements in a given territory and thus, might be an innovative tool to decrease human-wildlife conflicts.     

Vocal coordination of troop movement among white-faced capuchin monkeys,Cebus capucinus

Coordinated travel by social groups is well documented, often with evidence that cognitive spatial maps are employed. Yet the mechanisms by which movement decisions are made and implemented within social groups are poorly known. In a field study of white-faced capuchin monkeys in Costa Rica it was demonstrated that a specific call, the “trill,” is used by adults in the initiation and directing of troop movement. The trills of subadults were restricted to vocal exchanges with other subadults. Continuous vocal recordings were collected of the vocalizations of the 14 members of the study troop. A cumulative 33.7 h of continuous samples and 1,892 sonagrams were analyzed. In addition to vocalizations clearly associated with alarm, distress, or agonistic contexts, two distinct call types were identified, trills and huhs. Age-sex classes differed in the rate at which both types of calls were produced in different spatial positions within the troop. Adult females and males produced higher rates of trills when in the leading edge compared to all other spatial positions in a traveling troop. Trills at the edge of a stationary troop represented 36 “successful” and 3 “unsuccessful” start attempts; the troop usually moved in the trajectory predicted by a trilling adult's location on the troop periphery within 10 min of the initiation of trilling. Adults also altered the trajectory of traveling troops by trilling at the side and back of the troop (10 “successful” and 4 “unsuccessful” attempts). Huh vocalizations were most predictably produced when a capuchin is in a dense fruit patch. These results emphasize the role vocalizations serve in the coordination and trajectory of group movement in nonhuman primates, especially those populations that are arboreal or in which visual contact is otherwise impeded. © 1993 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Is Leadership a Reliable Concept in Animals? An Empirical Study in the Horse

Leadership is commonly invoked when accounting for the coordination of group movements in animals, yet it remains loosely defined. In parallel, there is increased evidence of the sharing of group decisions by animals on the move. How leadership integrates within this recent framework on collective decision-making is unclear. Here, we question the occurrence of leadership in horses, a species in which this concept is of prevalent use. The relevance of the three main definitions of leadership – departing first, walking in front travel position, and eliciting the joining of mates – was tested on the collective movements of two semi-free ranging groups of Przewalski horses (Equus ferus przewalskii). We did not find any leader capable of driving most group movements or recruiting mates more quickly than others. Several group members often displayed pre-departure behaviours at the same time, and the simultaneous departure of several individuals was common. We conclude that the decision-making process was shared by several group members a group movement (i.e., partially shared consensus) and that the leadership concept did not help to depict individual departure and leading behaviour across movements in both study groups. Rather, the different proxies of leadership produced conflicting information about individual contributions to group coordination. This study discusses the implications of these findings for the field of coordination and decision-making research.     

Dominance and affiliation as factors in the social organization of same-sex groups of elementary school children

The interactional patterns among first- and second- grade children in same-sex activity groups were analyzed in order to describe the relationships among several aspects of social organization and to examine the centrality of dominance and affiliation in social organization. Videotapes of one group of boys (N = 12) and one group of girls (N = 12) were coded. The results indicated that for both male and female groups, it was possible to specify dominance, leadership initiation, and leadership organization hierarchies. Moreover, there was a highly convergent pattern among multiple indicators of social organization centering on dominance and affiliation. However, the correlation patterns after controlling for social play suggested that the initially similar patterns were accounted for in different ways. Among the girls, the primary element linking the various dimensions was level of social play. Among the boys, there remained a smaller yet interrelated network indicating regularity in rank position for dominance, successful bids, recipient of requests, and number of play partners.     

How many for dinner? Recruitment and monitoring by glances in capuchins

Group members present physical and physiological differences according to their age, sex or social status, which could generate motivation differences among individuals during travel. In spite of these divergences of interest among individuals, the group succeeds more often than not in making a collective decision about departure time and which direction to take. To reach a consensus decision, animals should exchange information relating to characteristics of group movement through different communication channels. The main purpose of this study is to understand the function of behaviour patterns displayed during movements of white-faced capuchins (Cebus capucinus). We designed experiments in which we provoked collective movements involving a binary choice. During experiments, a video camera recorded the behaviour of each capuchin, which enabled us to determine which individuals displayed a behavioural pattern during travel and how this behaviour influenced the other group members. We found that looking backwards seemed to permit the recruitment of group mates during collective movement. This behaviour also seemed to allow the quantification of the number of followers, since the emitter modified its locomotion speed according to this number. In this preliminary study, we showed that visual behaviour was used to recruit and monitor group mates during collective movements and provided information on mechanisms involved in maintaining cohesion and coordination among group members during travel.     

The Organization of Collective Group Movements in Wild Barbary Macaques (Macaca sylvanus): Social Structure Drives Processes of Group Coordination in Macaques

Social animals have to coordinate activities and collective movements to benefit from the advantages of group living. Animals in large groups maintain cohesion by self-organization processes whereas in smaller groups consensus decisions can be reached. Where consensus decisions are relevant leadership may emerge. Variation in the organization of collective movements has been linked to variation in female social tolerance among macaque species ranging from despotic to egalitarian. Here we investigated the processes underlying group movements in a wild macaque species characterized by a degree of social tolerance intermediate to previously studied congeneric species. We focused on processes before, during and after the departure of the first individual. To this end, we observed one group of wild Barbary macaques (Macaca sylvanus) in the Middle Atlas, Morocco using all-occurrence behaviour sampling of 199 collective movements. We found that initiators of a collective movement usually chose the direction in which more individuals displayed pre-departure behavior. Dominant individuals contributed to group movements more than subordinates, especially juveniles, measured as frequencies of successful initiations and pre-departure behaviour. Joining was determined by affiliative relationships and the number of individuals that already joined the movement (mimetism). Thus, in our study group partially shared consensus decisions mediated by selective mimetism seemed to be prevalent, overall supporting the suggestion that a species’ social style affects the organization of group movements. As only the most tolerant species show equally shared consensus decisions whereas in others the decision is partially shared with a bias to dominant individuals the type of consensus decisions seems to follow a stepwise relation. Joining order may also follow a stepwise, however opposite, relationship, because dominance only determined joining in highly despotic, but not in intermediate and tolerant species.     

Female Coordination of Group Travel in Wild Propithecus and Eulemur

Coordination of primate group movements by individual group members is generally categorized as leadership behavior, which entails several steps: deciding where to move next, initiating travel, and leading a group between food, water sources, and rest sites. Presumably, leaders are able to influence their daily foraging efficiency and nutritional intake, which could influence an individual's feeding ecology and long-term reproductive success. Within anthropoid species, females lead group movements in most female-bonded groups, while males lead groups in most nonfemale-bonded groups. Group leadership has not been described for social prosimians, which are typically not female-bonded. We describe group movements in two nonfemale-bonded, lemurid species living in southeastern Madagascar, Propithecus diadema edwardsi and Eulemur fulvus rufus. Although several social lemurids exhibit female dominance Eulemur fulvus rufus does not, and evidence for female dominance is equivocal in Propithecus diadema edwardsi. Given the ecological stresses that females face during reproduction, we predict that females in these two species will implement alternative behavioral strategies such as group leadership in conjunction with, or in the absence of, dominance interactions to improve access to food. We found that females in both species initiated and led group movements significantly more often than males did. In groups with multiple females, one female was primarily responsible for initiating and leading group movements. We conclude that female nutritional needs may determine ranging behavior to a large extent in these prosimian species, at least during months of gestation and lactation.     

Leadership in Moving Human Groups

How is movement of individuals coordinated as a group? This is a fundamental question of social behaviour, encompassing phenomena such as bird flocking, fish schooling, and the innumerable activities in human groups that require people to synchronise their actions. We have developed an experimental paradigm, the HoneyComb computer-based multi-client game, to empirically investigate human movement coordination and leadership. Using economic games as a model, we set monetary incentives to motivate players on a virtual playfield to reach goals via players'' movements. We asked whether (I) humans coordinate their movements when information is limited to an individual group member''s observation of adjacent group member motion, (II) whether an informed group minority can lead an uninformed group majority to the minority''s goal, and if so, (III) how this minority exerts its influence. We showed that in a human group – on the basis of movement alone – a minority can successfully lead a majority. Minorities lead successfully when (a) their members choose similar initial steps towards their goal field and (b) they are among the first in the whole group to make a move. Using our approach, we empirically demonstrate that the rules of swarming behaviour apply to humans. Even complex human behaviour, such as leadership and directed group movement, follow simple rules that are based on visual perception of local movement.     

Self-Organization in Primates: Understanding the Rules Underlying Collective Movements

Patterns of collective movements, such as the distribution of leadership and the organization of individuals, may be either homogeneously (no leader, no specific order), or heterogeneously (1 or several leaders, and a highly stable order) distributed. Members of a group need to synchronize their activities and coordinate their movements, despite the fact that they differ in physiological or morphological traits. The degree of difference in these traits may affect their decision-making strategy. We demonstrate how a theoretical model based on a variation of a simple mimetic rule, i.e., an amplification process, can result in each of the various collective movement patterns and decision-making strategies observed in primates and other species. We consider cases in which 1) the needs of different individuals are identical and social relationships are equivalent between group members, 2) the needs of individuals are different and social relationships are equivalent, and 3) the needs of individuals are different and social relationships are different. Finally, 4) we assess how the synergy between 2 mimetism rules, specifically the probability of joining a movement and that of canceling an initiation, allows group members to stay synchronized and cohesive. Our models suggest that similar self-organized processes have been selected as reliable and well-adapted means for optimal collective decisions across species, despite differences in their biological and social characteristics.     

Decision-making processes: The case of collective movements

Besides focusing on the adaptive significance of collective movements, it is crucial to study the mechanisms and dynamics of decision-making processes at the individual level underlying the higher-scale collective movements. It is now commonly admitted that collective decisions emerge from interactions between individuals, but how individual decisions are taken, i.e. how far they are modulated by the behaviour of other group members, is an under-investigated question. Classically, collective movements are viewed as the outcome of one individual's initiation (the leader) for departure, by which all or some of the other group members abide. Individuals assuming leadership have often been considered to hold a specific social status. This hierarchical or centralized control model has been challenged by recent theoretical and experimental findings, suggesting that leadership can be more distributed. Moreover, self-organized processes can account for collective movements in many different species, even in those that are characterized by high cognitive complexity. In this review, we point out that decision-making for moving collectively can be reached by a combination of different rules, i.e. individualized (based on inter-individual differences in physiology, energetic state, social status, etc.) and self-organized (based on simple response) ones for any species, context and group size.     

Sex differences in leadership during group movement in mantled howler monkeys (Alouatta palliata)

Benefits of group life depend in large part on whether animals remain cohesive, which often requires collective decisions about where and when to move. During a group movement, the leader may be considered as the individual occupying the vanguard position of the group progression, when its movement evokes following by other group members. In nondespotic societies, individuals with greater incentives to move frequently are leaders. During 15 months of observations (1,712 contact hours), we investigated two mantled howler monkey (Alouatta palliata) groups at La Flor de Catemaco (Los Tuxtlas, Mexico) to examine whether sex and female reproductive state influenced leadership likelihood in two contexts: movements toward feeding trees; movements associated with loud calls, a group-defense behavior used by males of this genus. Females led and occupied forward positions during group movements toward feeding trees more often than adult males. Adult females led these movements more frequently when they were gestating than when they were lactating or cycling. There were no differences between sexes in the leadership of group movements associated with loud calls. Leadership by gestating females is perhaps the result of their higher nutritional/energetic needs when compared with cycling females, and of their greater mobility when compared with lactating females carrying dependent offspring. Female leadership during movements toward feeding trees may be a mechanism to optimize access to food resources in mantled howler monkeys.     

The initiation factor 3 (IF3) residues interacting with initiator tRNA elbow modulate the fidelity of translation initiation and growth fitness in Escherichia coli

Initiation factor 3 (IF3) regulates the fidelity of bacterial translation initiation by debarring the use of non-canonical start codons or non-initiator tRNAs and prevents premature docking of the 50S ribosomal subunit to the 30S pre-initiation complex (PIC). The C-terminal domain (CTD) of IF3 can carry out most of the known functions of IF3 and sustain Escherichia coli growth. However, the roles of the N-terminal domain (NTD) have remained unclear. We hypothesized that the interaction between NTD and initiator tRNA^fMet (i-tRNA) is essential to coordinate the movement of the two domains during the initiation pathway to ensure fidelity of the process. Here, using atomistic molecular dynamics (MD) simulation, we show that R25A/Q33A/R66A mutations do not impact NTD structure but disrupt its interaction with i-tRNA. These NTD residues modulate the fidelity of translation initiation and are crucial for bacterial growth. Our observations also implicate the role of these interactions in the subunit dissociation activity of CTD of IF3. Overall, the study shows that the interactions between NTD of IF3 and i-tRNA are crucial for coupling the movements of NTD and CTD of IF3 during the initiation pathway and in imparting growth fitness to E. coli.     

Consistency of leadership in shoals of mosquitofish (Gambusia holbrooki) in novel and in familiar environments

In social animal groups, an individual's spatial position is a major determinant of both predation risk and foraging rewards. Additionally, the occupation of positions in the front of moving groups is generally assumed to correlate with the initiation of group movements. However, whether some individuals are predisposed to consistently occupy certain positions and, in some instances, to consistently lead groups over time is as yet unresolved in many species. Using the mosquitofish (Gambusia holbrooki), we examined the consistency of individuals' spatial positions within a moving group over successive trials. We found that certain individuals consistently occupied front positions in moving groups and also that it was typically these individuals that initiated group decisions. The number of individuals involved in leading the group varied according to the amount of information held by group members, with a greater number of changes in leadership in a novel compared to a relatively familiar environment. Finally, our results show that the occupation of lead positions in moving groups was not explained by characteristics such as dominance, size or sex, suggesting that certain individuals are predisposed to leadership roles. This suggests that being a leader or a follower may to some extent be an intrinsic property of the individual.     

Initiative, personality and leadership in pairs of foraging fish

Studies of coordinated movement have found that, in many animal species, bolder individuals are more likely to initiate movement and shyer individuals to follow. Here, we show that in pairs of foraging stickleback fish, leadership is not merely a passive consequence of temperamental differences. Instead, the act of initiating a joint foraging trip out of cover itself brings about a change in the role that an individual plays throughout the subsequent trip, and success in recruiting a partner affects an individual's tendency to initiate the next trip. On each joint trip, whichever fish took the initiative in leading out of cover gains greater influence over its partner's behaviour, which persists even after several changes in position (i.e. termination attempts and re-joining). During any given trip, the initiator is less responsive to its partner's movements than during trips initiated by the partner. An individual's personality had an important effect on its response to failure to recruit a partner: while bold fish were unaffected by failures to initiate a joint trip, shy individuals were less likely to attempt another initiation after a failure. This difference provides a positive feedback mechanism that can partially stabilise social roles within the pair, but it is not strong enough to prevent occasional swaps, with individuals dynamically adjusting their responses to one another as they exchange roles.     

Social Structure Affects Initiations of Group Movements but Not Recruitment Success in Japanese Macaques (<Emphasis Type="Italic">Macaca fuscata</Emphasis>)

Research on collective movements has often focused on the sociodemographic parameters explaining the success of some individuals as leaders or initiators of collective movements. Several of these studies have shown the influence of social structure, through kinship and affiliative relationships, on the organization of collective movements. However, these studies have been conducted on semi-free-ranging groups of macaques that were not faced with a natural environment and its constraints. In the socially intolerant rhesus macaque (Macaca mulatta) the success of an initiator correlates with its hierarchical rank, the most dominant individuals being the most successful. We investigated the collective movements of another socially intolerant macaque species, Japanese macaques, in the wild, to assess whether the social structure was still a determinant factor under natural conditions. In line with previous studies of macaques, we found that social structure drove the organization of collective movements. More dominant individuals initiated more collective movements. However, dominance did not affect the success of an initiation, i.e., the number of individuals joining. In addition, kinship strongly constrained the associations observed in females during collective movements. These results reflect the social structure of Japanese macaques, in which strong power asymmetry and kinship relationships constrain the majority of interactions between individuals within the group. Moreover, these results are similar to those observed in semi-free-ranging rhesus macaques and support the hypothesis of an effect of social determinants on collective movements of primates even under natural conditions.     

The dynamic cycle of bacterial translation initiation factor IF3

Initiation factor IF3 is an essential protein that enhances the fidelity and speed of bacterial mRNA translation initiation. Here, we describe the dynamic interplay between IF3 domains and their alternative binding sites using pre-steady state kinetics combined with molecular modelling of available structures of initiation complexes. Our results show that IF3 accommodates its domains at velocities ranging over two orders of magnitude, responding to the binding of each 30S ligand. IF1 and IF2 promote IF3 compaction and the movement of the C-terminal domain (IF3C) towards the P site. Concomitantly, the N-terminal domain (IF3N) creates a pocket ready to accept the initiator tRNA. Selection of the initiator tRNA is accompanied by a transient accommodation of IF3N towards the 30S platform. Decoding of the mRNA start codon displaces IF3C away from the P site and rate limits translation initiation. 70S initiation complex formation brings IF3 domains in close proximity to each other prior to dissociation and recycling of the factor for a new round of translation initiation. Altogether, our results describe the kinetic spectrum of IF3 movements and highlight functional transitions of the factor that ensure accurate mRNA translation initiation.     

Participant Profiling and Pattern of Crop-Foraging in Chacma Baboons (<Emphasis Type="Italic">Papio hamadryas ursinus</Emphasis>) in Zimbabwe: Why Does Investigating Age–Sex Classes Matter?

Transformation and loss of natural habitat to urbanization and agriculture provide new opportunities for primates to feed on anthropogenic food sources. Currently, mitigation strategies fail to target the individuals responsible for initiating and maintaining this behavior. As primates mainly forage on crops in groups, we investigate the crop-foraging behavior of a group of 40 chacma baboons in Zimbabwe from the perspective of collective movements, i.e., when a group of animals move together in the same direction, thus resulting in a change of location. We collected data on 110 crop-foraging events during 35 days in March–April 2014. We recorded baboon movement and behavior with a camcorder and obtained further information through video analysis. Most crop-foraging events involved less than 20% of the troop and lasted less than 3 min. Although crop-foraging parties were composed of all age–sex classes, adult females and particularly adult males initiated most crop-foraging events and made direct movements (without stopping on the road) more often than nonadult participants. Baboons made up to five successive attempts to crop forage in a single crop-foraging event. Neither the number of participants nor the success of the crop-foraging events increased over the successive attempts. Finally, crop-foraging events were more successful and more frequent in unguarded areas than in guarded areas. These results suggest that group members are highly synchronized and that crop-foraging is based on a collective decision such as classical foraging movements. In addition, the short duration of the crop-foraging events might prevent detection of baboons by farmers. The more frequent initiation of crop-foraging by adults compared to nonadults might be explained by greater energetic needs or a greater tendency of adults to take risks. These preliminary data can help inform long-term strategies for farmers to reduce crop losses to baboons, as guarding helps reduce damage but does not prevent it.     

Coordination of Group Movements in Wild Red-fronted Lemurs (<Emphasis Type="Italic">Eulemur rufifrons</Emphasis>): Processes and Influence of Ecological and Reproductive Seasonality

Group-living species have to coordinate collective actions to maintain cohesion. In primates, spatial movements represent a meaningful model to study group coordination processes across different socio-ecological contexts. We studied 4 groups of red-fronted lemurs (Eulemur rufifrons) in Kirindy Forest, Madagascar, between 2008 and 2010 across different ecological and reproductive seasons. We collected data on ranging patterns using GPS collars and observational data on different predefined parameters of group movements, including initiation, leadership, followership, overtaking events, termination, and travel distances. Cohesion of these relatively small, egalitarian lemur groups was high year-round, but daily path length and home range size varied considerably between ecological seasons, presumably due to long-distance migrations of some groups at the beginning of the rainy season. Individuals of different age and sex classes successfully initiated group movements. However, stable female leadership prevailed year-round, irrespective of ecological and reproductive season, which might be due to higher or more specific energetic requirements of reproduction. In contrast to lemur species with a more despotic social structure, female red-fronted lemurs did not recruit more followers than males. Adult leaders recruited more followers than subadult ones. Further, recruitment success was higher during the peak of the dry season, when predation risk appeared to be higher. Distances of single group movements did not depend on the initiator’s sex and age or on ecological seasons. Our results provide new insights into seasonal variability of coordination processes and the role of social dominance in lemur group movements, thereby contributing to a comparative perspective from a primate radiation that evolved group living independently of anthropoids.