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Changes in marine ecosystems are easier to detect in upper‐level predators, like seabirds, which integrate trophic interactions throughout the food web.Here, we examined whether diving parameters and complexity in the temporal organization of diving behavior of little penguins (Eudyptula minor) are influenced by sea surface temperature (SST), water stratification, and wind speed—three oceanographic features influencing prey abundance and distribution in the water column.Using fractal time series analysis, we found that foraging complexity, expressed as the degree of long‐range correlations or memory in the dive series, was associated with SST and water stratification throughout the breeding season, but not with wind speed. Little penguins foraging in warmer/more‐stratified waters exhibited greater determinism (memory) in foraging sequences, likely as a response to prey aggregations near the thermocline. They also showed higher foraging efficiency, performed more dives and dove to shallower depths than those foraging in colder/less‐stratified waters.Reductions in the long‐term memory of dive sequences, or in other words increases in behavioral stochasticity, may suggest different strategies concerning the exploration–exploitation trade‐off under contrasting environmental conditions., Little penguins foraging in warmer/more‐stratified waters exhibited less stochastic foraging sequences likely as a response to prey aggregations nearby the thermocline. Ultimately, they showed higher foraging efficiency and numbers of dives, and lower mean dive depths than those foraging in colder/less‐stratified waters.

Long-range signaling, such as acoustic communication, is best understood within the broader context of all potential receivers. Exactly what kind of information is transmitted or obtained is a matter of debate. To address this issue, we describe the communication network of a population of wild siamangs (Symphalangus syndactylus), small territorial apes that sing loud and complex duets. Based on calling data collected over >3400 observation hours on 7 groups of wild siamangs, we used linear mixed-effects models to evaluate the effect of changes in group composition on singing rates and social network analysis to study the effect of social change on the structure of this siamang communication network. Results show that, compared to stable groups, groups whose composition had recently changed elicited significantly more responses to their calls from neighboring groups. These results support the hypothesis that listening individuals can take advantage of public information to detect points of social instability in the community, e.g., adult males seeking opportunities to obtain their own territory. Our results help explain some sociobiological conundrums concerning hylobatids, e.g., by highlighting a potential strategic benefit for males living in the multimale, single female groups that are reported in some species, advance our understanding of the function of calling in hylobatids, and offer theoretical and methodological insights applicable to other taxa such as birds and cetaceans.

Whilst fundamental to human societies, collective decision-making such as voting systems can lead to non-efficient decisions, as past climate policies demonstrate. Current systems are harshly criticised for the way they consider voters needs and knowledge. Collective decision-making is central in human societies but also occurs in animal groups mostly when animals need to choose when and where to move. In these societies, animals balance between the needs of the group members and their own needs and rely on each individuals (partial) knowledge. We argue that non-human animals and humans share similar collective decision processes, among which are agenda-setting, deliberation and voting. Recent works in artificial intelligence have sought to improve decision-making in human groups, sometimes inspired by animals decision-making systems. We discuss here how our societies could benefit from recent advances in ethology and artificial intelligence to improve our collective decision-making system. published

Resources that are embedded in social relationships, such as shared knowledge, access to food, services, social support or cooperation, are all examples of social capital. Social capital is recognized as an important age-related mediator of health in humans and of fitness-related traits in animals. A rich social capital in humans can slow senescence and reverse age-related deficits. Animals have been shown to adjust their social capital at different life stages (i.e., early, reproductive and post-reproductive life), which may promote individual fitness. However, the underlying biological mechanisms remain unknown. We suggest future research avenues to focus on social capital as a modifiable dimension to gain a better understanding of variations in senescence, and thereby provide new approaches to promote healthy ageing.

The study of non-human multilevel societies can give us insights into how group-level relationships function and are maintained in a social system, but their mechanisms are still poorly understood. The aim of this study was to apply spatial association data obtained from drones to verify the presence of a multilevel structure in a feral horse society. We took aerial photos of individuals that appeared in pre-fixed areas and collected positional data. The threshold distance of the association was defined based on the distribution pattern of the inter-individual distance. The association rates of individuals showed bimodality, suggesting the presence of small social organizations or “units”. Inter-unit distances were significantly smaller than those in randomly replaced data, which showed that units associate to form a higher-level social organization or “herd”. Moreover, this herd had a structure where large mixed-sex units were more likely to occupy the center than small mixed-sex units and all-male-units, which were instead on the periphery. These three pieces of evidence regarding the existence of units, unit association, and stable positioning among units strongly indicated a multilevel structure in horse society. The present study contributes to understanding the functions and mechanisms of multilevel societies through comparisons with other social indices and models as well as cross-species comparisons in future studies., 野生化したウマの重層社会をドローンからの観察により解明. 京都大学プレスリリース. 2021-01-18.

Previous primate social network studies largely limited their focus to grooming and/or aggression networks, particularly among adult females. In addition, the consistency of individuals' network centrality across time and/or different networks has received little attention, despite this being critical for a global understanding of dynamic social structure. Here, we analyzed the grooming, aggression, and play social networks of a group of 26-28 wild vervet monkeys (Chlorocebus pygerythrus), including adults and juveniles, over two periods of 6 months. We collected data on grooming, play, and aggression using focal animal sampling with instantaneous recording and ad libitum sampling. We examined whether individuals' network centralities were consistent over the two periods and across networks, as well as the effect of age, sex, and dominance rank on three individual centrality metrics in each network and within each study period. We found that individuals were quite consistent in their network position from 1 year to the next despite changes in group composition. However, their network centralities were not correlated across networks, except for Strength and weighted Eigenvector centrality between grooming and aggression networks. We also found that in the aggression network, high-rankers showed the highest centrality in most network metrics (e.g., Degree, Strength, and Eigenvector centrality) and compared to males, females were most central in 2017 but not in 2018. In the grooming network, high-ranking females had the highest Eigenvector centrality, whereas in the play network, juvenile males had the highest Eigenvector centrality. Our findings corroborate previous findings on vervet monkeys. In addition, they show that individuals' network centralities may vary among networks and over time; thus highlighting the effect of sociodemographics and behaviors' functions on the group level dynamics of social behavior.

In social networks analysis, two different approaches have predominated in creating null models for hypothesis testing, namely pre‐network and node network permutation approaches. Although the pre‐network permutation approach appears more advantageous, its use has mainly been restricted to data on associations and sampling methods such as ‘group follows’. The pre‐network permutation approach has recently been adapted to data on interactions and the focal sampling method, but its performance in different scenarios has not been thoroughly explored. Here, we assessed the performance of the pre‐network and node network permutation approach in several simulated scenarios based on proneness to false positive or false negatives and with or without observation bias. Our results showed that the pre‐network permutation was sensitive to false positives in scenarios with or without observation bias. The node network permutation approach produced fewer false positives and negatives than the pre‐network approach, but only in scenarios without observation bias. In scenarios with observation bias, the node network permutation approach was outperformed by pre‐network permutation. Caution should be taken when using the pre‐network and node network permutations to create null models with data collected via focal sampling. This study provides future methodological research perspectives for social network analyses. publishedVersion

International audience; Social information and socially transmitted pathogens are governed by social structure, and also shape social interactions. However, information and infection are rarely investigated as interactive factors driving social evolution. We propose exactly such an integrative framework, drawing attention to mechanisms of social phenotypic plasticity for information spread and pathogen control.

From a cognitive point of view, management and knowledge of social relationships is thought to be very challenging. Because of ecological and demographic constraints, relationships are likely to be prone to variation and hence need constant updating. Social network analysis is a potential tool to quantify the information that needs to be processed. However, despite the growing number of studies on social networks, few have focused on their dynamics and how they evolve across time. Here we present one of the rare studies that tests the influence of demographic variation on social relationships' stability through temporal analysis. Using field data collected on three wild groups of vervet monkeys, Chlorocebus aethiops, we first analysed the relationships' stability by running correlations between 3-month periods. Then, we investigated how natural demographic variation changed individual centralities (eigenvector) and strength of dyadic relationships within both grooming and proximity networks over a period of 2 years. In vervets, females are philopatric, while males emigrate from their natal group. Thus, we tested whether changes in demography had more influence on network centrality measures and relationship strength in females and their juveniles than in males. Correlations between periods yielded no evidence that predictability of future relationship quality declined with time from current relationship quality. In addition, male immigration was mostly responsible for increases in the core group members' centrality while male emigration had the opposite effect. Regarding dyadic relationships, we found inconsistent patterns that varied with respect to how age/sex and immigration/disappearance affected the network studied (grooming versus proximity). Our findings support the idea that social networks are dynamic structures that vary through time. Similar analyses on other species are needed to investigate which network features emerge as candidates responsible for variation in the complexity with which individuals keep track of relationships.

In most eusocial insects, the division of labour results in relatively few individuals foraging for the entire colony. Thus, the survival of the colony depends on its efficiency in meeting the nutritional needs of all its members. Here, we characterise the network topology of a eusocial insect to understand the role and centrality of each caste in this network during the process of food dissemination. We constructed trophallaxis networks from 34 food-exchange experiments in black garden ants (Lasius niger). We tested the influence of brood and colony size on (i) global indices at the network level (i.e. efficiency, resilience, centralisation and modularity) and (ii) individual values (i.e. degree, strength, betweenness and the clustering coefficient). Network resilience, the ratio between global efficiency and centralisation, was stable with colony size but increased in the presence of broods, presumably in response to the nutritional needs of larvae. Individual metrics highlighted the major role of foragers in food dissemination. In addition, a hierarchical clustering analysis suggested that some domestics acted as intermediaries between foragers and other domestics. Networks appeared to be hierarchical rather than random or centralised exclusively around foragers. Finally, our results suggested that networks emerging from social insect interactions can improve group performance and thus colony fitness., info:eu-repo/semantics/published

International audience; Organisms living in hot, arid environments face important risks associated with hyperthermia and dehydration which are expected to become more severe with climate change. To mitigate these risks, individuals often modify behaviour, e.g. reducing activity and seeking shade. These behavioural modifications may affect interactions between individuals, with consequences for the social structure of groups. We tested whether the social structure of cooperative groups of sociable weavers (Philetairus socius) varied with environmental temperature. We recorded the nature and frequency of interactions at feeders positioned beneath three sociable weaver colonies (N = 49 identified birds) in the Kalahari Desert with respect to environmental temperatures over a 30‐day period. Using random forest models, we examined whether thermal conditions predicted variation in social network structure. We also conducted focal observations of individual weavers to assess functional links between temperature, intensity of heat dissipation behaviour (panting), and immediate effects on social behaviour. Our results suggest that the social structure of weaver colonies becomes less cohesive and more fragmented at extreme and variable environmental temperatures. These changes in network structure appear to be linked with individuals’ heat dissipation behaviour: extreme and variable temperatures were associated with increased panting, which was significantly correlated with an immediate reduction in the frequency of association. Collectively, our results indicate that interactions within groups could be disturbed by environmental temperature variation and extremes. Changing temperature regimes could therefore affect the functioning of animal societies by altering social networks.

International audience; In social species, network centralities of group members shape social transmission and other social phenomena. Different factors have been found to influence the measurement of social networks, such as data collection and observation methods. In this study, we collected data on adults and juveniles and examined the effect of data collection method (ad libitum sampling vs. focal animal sampling) and observation method (interaction—grooming; play—vs. association—arm‐length; 2 m; 5 m proximities—) on social networks in wild vervet monkeys. First, we showed using a bootstrapping method, that uncertainty of ad libitum grooming and play matrices were lesser than uncertainty of focal matrices. Nevertheless, grooming and play networks constructed from ad libitum and focal animal sampling were very similar and highly correlated. We improved the certainty of both grooming and play networks by pooling focal and ad libitum matrices. Second, we reported a high correlation between the proximity arm‐length network and the focal grooming one making an arm‐length proximity network a reasonable proxy for a grooming one in vervet monkeys. However, we did not find such a correlation between proximity networks and the play one. Studying the effects of methodological issues as data collection and observation methods can help improve understanding of what shapes social networks and which data collection method to choose to study sociality.

The extent of differentiation of social relationships within groups is a means to assess social complexity, with greater differentiation indicating greater social complexity. Socio-ecological factors are likely to influence social complexity, but no attempt has been made to explain the differentiation of social relationships using multiple socio-ecological factors. Here, we propose a conceptual framework based on four components underlying multiple socio-ecological factors that influence the differentiation of social relationships: the extent of within-group contest competition to access resources, the extent to which individuals differ in their ability to provide a variety of services, the need for group-level cooperation and the constraints on social interactions. We use the framework to make predictions about the degree of relationship differentiation that can be expected within a group according to the cumulative contribution of multiple socio-ecological factors to each of the four components. The framework has broad applicability, since the four components are likely to be relevant to a wide range of animal taxa and to additional socio-ecological factors not explicitly dealt with here. Hence, the framework can be used as the basis for the development of novel and testable hypotheses about intra- and interspecific differences in relationship differentiation and social complexity.

Social structure can theoretically regulate disease risk by mediating exposure to pathogens via social proximity and contact. Investigating the role of central individuals within a network may help predict infectious agent transmission as well as implement disease control strategies, but little is known about such dynamics in real primate networks. We combined social network analysis and a modeling approach to better understand transmission of a theoretical infectious agent in wild Japanese macaques, highly social animals which form extended but highly differentiated social networks. We collected focal data from adult females living on the islands of Koshima and Yakushima, Japan. Individual identities as well as grooming networks were included in a Markov graph-based simulation. In this model, the probability that an individual will transmit an infectious agent depends on the strength of its relationships with other group members. Similarly, its probability of being infected depends on its relationships with already infected group members. We correlated: (i) the percentage of subjects infected during a latency-constrained epidemic; (ii) the mean latency to complete transmission; (iii) the probability that an individual is infected first among all group members; and (iv) each individual's mean rank in the chain of transmission with different individual network centralities (eigenvector, strength, betweenness). Our results support the hypothesis that more central individuals transmit infections in a shorter amount of time and to more subjects but also become infected more quickly than less central individuals. However, we also observed that the spread of infectious agents on the Yakushima network did not always differ from expectations of spread on random networks. Generalizations about the importance of observed social networks in pathogen flow should thus be made with caution, since individual characteristics in some real world networks appear less relevant than they are in others in predicting disease spread. Am. J. Primatol. 78:767-779, 2016. © 2016 Wiley Periodicals, Inc.

Intranidal food dissemination through trophallactic exchanges is a fundamental issue in social insect colonies but its underlying mechanisms are far from being clear. In light of the division of work, network theory and collective food management we develop a framework to investigate the spatiotemporal dynamics of the trophallactic network in starved Lasius niger ant colonies. Thanks to tracking methods we are able to record spatial locations of the trophallactic interactions in the nest. We highlight quantitative differences between the foragers and non-foragers concerning their contributions, their roles (donor/recipient) and their spatial distributions. Moreover, at the intracaste level, we show interindividual differences in all activities and we characterise their nature. In particular, within each caste, all the individuals have the same probability to start their food exchange activity but their probability to exchange differs after their first trophallactic event. Interestingly, despite the highlighted interindividual differences, the trophallactic network does not differ from a random network., SCOPUS: ar.j, info:eu-repo/semantics/published

International audience; The use of social network analysis to better understand animal behaviour has led to anincrease in the number of studies on this topic, particularly for species management andconservation as well as the welfare of captive animals. The current knowledge of social organizationin the European bison (Bison bonasus) is still largely based on descriptions of group compositions,most of which were obtained during opportunistic field observations. However, the numerousconservation programs for this species can only implement effective management decisions after theanalysis of its social structures. For instance, the removal of a key individual can disturb the socialstability of a group and thus indirectly affect the fitness of group members. This is the first study thatuses social network analysis to examine the social structure of a semi-free ranging bison herd (N =14). Closest neighbour associations are used to calculate the eigenvector centrality and individualsocial strength of each animal. These two indices are combined after a principal component analysis(PCA) to form the Sociability variable, which was then tested for correlations with age, dominancerank, number of matrilines and reproductive status (lactating vs non-lactating). Results reveal stronggroup cohesion, with a close association of individuals belonging to the same matriline within theherd. The cumulative distribution of the eigenvector centralities follows a linear function, meaningthat no individual has a highly central position compared to its congeners. Finally, a high Sociabilityvalue was not correlated to age, dominance rank or number of matrilines, but was dependent on thereproductive status of females. These results indicate the necessity to consider the social welfare ofanimals, for instance by taking matrilineal relationships into account when making bison groupsmanagement decisions.

International audience; Dilution of predation risk within groups allows individuals to be less vigilant and forage more while still facing lower risk than if they were alone. How group size influences vigilance when individuals can also adjust their space use and whether this relationship differs among individuals contributing differently to space use decisions remain unknown. We present a model-based study of how dilution affects the optimal antipredator behavior of group members in groups where all individuals determine their vigilance level while group leaders also determine space use. We showed that optimal vigilance did not always decrease with group size, as it was sometimes favorable for individuals in larger groups to use riskier patches while remaining vigilant. Followers were also generally less vigilant than leaders. Indeed, followers needed to acquire more resources than leaders, as only the latter could decide when to go to richer patches. Followers still benefit from dilution of predation risk compared with solitary individuals. For leaders, keeping their leadership status can be more important than incorporating new group members to increase dilution. We demonstrate that risk dilution impacts both optimal vigilance and space use, with fitness reward being tied to a member's ability to influence group space use.

International audience; The concept of directed social learning predicts that social learning opportunities for an individual will depend on social dynamics, context and demonstrator identity. However, few empirical studies have examined social attention biases in animal groups. Sex-based and kinship-based biases in social learning and social attention towards females have been shown in a despotic and female philopatric primate: the vervet monkey (Chlorocebus pygerythrus). The present study examined social attention during the juvenile period. Social attention was recorded through 5-min focal observations during periods of natural foraging. Kin emerged as the most important focus of social attention in juveniles, intensified by biased spatial proximity towards matrilineal related members. The highest-ranking conspecifics were more frequently observed by juveniles than low-ranking ones. Additionally, younger and orphaned juveniles showed higher levels of social attention overall, compared to other age categories. No effect of the juvenile’s hierarchical rank was detected, suggesting that the variation in social attention recorded reflects different biases and stages of social learning and socialisation, rather than social anxiety. Juvenile females tended to exhibit a dominance-based bias more strongly than did males. This might be explained by a greater emphasis on attaining social knowledge during juvenile socialisation in the philopatric sex. Moreover, despite a preferred association between juveniles, social attention was more often directed to adults, suggesting that adults may still be more often chosen as a target of attention independent of their dominance rank.

In myriad biological systems, multiple lines of evidence indicate that modularity, wherein parts of a network are organized into modules such as subgroups in animal networks, may affect social transmission processes. In animal societies, there is increased interest in understanding variation in the effects of modularity on transmission as it may provide important insight into a given network’s performance, in addition to the evolutionary consequences the structure of the network may have for individual fitness. Yet, to our knowledge, the degree to which network efficiency is modularity dependent has not yet been investigated in great detail in behavioral and evolutionary ecology. Here, we investigated to what degree network efficiency, as a proxy for social transmission, is modularity dependent. We created 2798 networks varying in group size and density, and tested whether network structure (density, Newman’s modularity, eigenvector centralization) and group size shape network efficiency. We also used published data from 41 primate social networks to test whether the predictions generated in our simulations were supported by empirical observations. Our results show a non-linear relationship between modularity and global efficiency, with the latter peaking at intermediate values of modularity in both theoretical and empirical networks. This phenomenon may have relevance for observed variation in social structure and its link with network performance. Our results may thus provide a basis from which to discuss the evolution of complex systems such as animal societies. Networks may maximize performance and minimize transmission costs, as demonstrated in neural networks, but to what degree network efficiency is modularity dependent has not yet been investigated in behavioral ecology. We provide evidence that modularity, such as subgrouping in animal networks, can have non-linear effects on transmission processes, with low values of modularity tending to positively influence social transmission and high values tending to negatively influence transmission. This pattern was consistent across small, medium, and large social groups from theoretical networks, and was corroborated by our empirical networks which were derived from 41 small- to medium-sized groups of 15 primate species. These results have potential implications for the understanding of social flexibility and its link with network performance, in addition informing many interdisciplinary fields, such as communication and computer science.

Followership is generally defined as a strategy that evolved to solve social coordination problems, and particularly those involved in group movement. Followership behavior is particularly interesting in the context of road-crossing behavior because it involves other principles such as risk-taking and evaluating the value of social information. This study sought to identify the cognitive mechanisms underlying decision-making by pedestrians who follow another person across the road at the green or at the red light in two different countries (France and Japan). We used agent-based modelling to simulate the road-crossing behaviors of pedestrians. This study showed that modelling is a reliable means to test different hypotheses and find the processes underlying decision-making when crossing the road. We found that two processes suffice to simulate pedestrian behaviors: Personal motivation and imitation. Importantly, the study revealed differences between the two nationalities and between sexes in the decision to follow and cross at the green and at the red light. Japanese pedestrians showed a greater mimetic behavior at the red light but the process takes into account both the number of crossing and waiting pedestrians, contrary to French citizens. Finally, the simulations are revealed to be similar to observations, not only for the departure latencies but also for the number of crossing pedestrians and the rates of illegal crossings. The conclusion suggests new solutions for safety in transportation research., SCOPUS: ar.j, info:eu-repo/semantics/published

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.

Sociality is suggested to evolve as a strategy for animals to cope with challenges in their environment. Within a population, each individual can be seen as part of a network of social interactions that vary in strength, type and dynamics (Sueur et al. 2011a). The structure of this social network can strongly impact upon not only on the fitness of individuals and their decision-making, but also on the ecology of populations and the evolution of a species. Our Franco-Japanese collaboration allowed us to study social networks in several species (Japanese macaques, chimpanzees, colobines, etc.) and on different topics (social epidemiology, social evolution, information transmission). Individual attributes such as stress, rank or age can affect how individuals take decisions and the structure of the social network. This heterogeneity is linked to the assortativity of individuals and to the efficiency of the flow within a network. It is important, therefore, that this heterogeneity is integrated in the process or pattern under study in order to provide a better resolution of investigation and, ultimately, a better understanding of behavioural strategies, social dynamics and social evolution. How social information affects decision-making could be important to understand how social groups make collective decisions and how information may spread throughout the social group. In human beings, road-crossing behaviours in the presence of other individuals is a good way to study the influence of social information on individual behaviour and decision-making, for instance. Culture directly affects which information - personal vs social - individuals prefer to follow. Our collaboration contributed to the understanding of the relative influence of different factors, cultural and ecological, on primate, including human, sociality.

Animals kept for livestock or conservation form strong cohesive groups when foraging and moving, in the same way as their wild counterparts. Collective decision-making involves making compromises by consensus to maintain group cohesion and synchronisation. This type of consensus can be observed during collective movements, when a leadership can emerge. In a distributed leadership, many group members may initiate collective movements but some individuals initiate more frequently than others and are more frequently followed by their conspecifics due to socio-demographic factors such as age, sex or dominance. In this study, we focused on organisation and leadership in the collective movements of semi-wild groups of Highland cattle ( Bos Taurus ). Highland cattle being often used in eco-pasture, studying leadership emergence and the use of space by animals may improve livestock and pastureland management. We studied nine different compositions (i.e., same location but with transfers of individuals) of four groups over a six-month period. The group sizes ranged from nine to 21 individuals. Results revealed that leadership is widely distributed in Highland cattle groups, with some individuals initiating more often than other group members. Indeed, in large groups, some group members never initiated movements. The number of followers within a movement was particularly influenced by the age of the initiator, its social centrality and dominance, but was also affected by the increase of pre-departure activities. This study also shows the influence of several variables on the joining rank of individuals during movement progression, such as age and social centrality. Finally, social centrality and the number of followers explained the departure latency between two individuals. Here, we proposed how these findings can help manage livestock.

Individual-based computer models show that different mechanisms, proximity-based or emotional bookkeeping, can lead to reciprocation. By comparing social networks from different computer models with those of empirical data, we show that the models’ social networks bear limited resemblance with some features of the observed social networks. This indicates that additional social processes (third-party awareness) may be needed in these models to represent more accurately the social behavior and interaction patterns observed in group-living animals.

International audience; Among nonhuman primates, the evolutionary underpinnings of variation in social structure remain debated, with both ancestral relationships and adaptation to current conditions hypothesized to play determining roles. Here we assess whether interspecific variation in higher‐order aspects of female macaque (genus: Macaca ) dominance and grooming social structure show phylogenetic signals, that is, greater similarity among more closely‐related species. We use a social network approach to describe higher‐order characteristics of social structure, based on both direct interactions and secondary pathways that connect group members. We also ask whether network traits covary with each other, with species‐typical social style grades, and/or with sociodemographic characteristics, specifically group size, sex‐ratio, and current living condition (captive vs. free‐living). We assembled 34–38 datasets of female‐female dyadic aggression and allogrooming among captive and free‐living macaques representing 10 species. We calculated dominance (transitivity, certainty), and grooming (centrality coefficient, Newman's modularity, clustering coefficient) network traits as aspects of social structure. Computations of K statistics and randomization tests on multiple phylogenies revealed moderate‐strong phylogenetic signals in dominance traits, but moderate‐weak signals in grooming traits. GLMMs showed that grooming traits did not covary with dominance traits and/or social style grade. Rather, modularity and clustering coefficient, but not centrality coefficient, were strongly predicted by group size and current living condition. Specifically, larger groups showed more modular networks with sparsely‐connected clusters than smaller groups. Further, this effect was independent of variation in living condition, and/or sampling effort. In summary, our results reveal that female dominance networks were more phylogenetically conserved across macaque species than grooming networks, which were more labile to sociodemographic factors. Such findings narrow down the processes that influence interspecific variation in two core aspects of macaque social structure. Future directions should include using phylogeographic approaches, and addressing challenges in examining the effects of socioecological factors on primate social structure.

Social play and grooming are typical affiliative interactions for many primate species, and are thought to have similar biological functions. However, grooming increases with age, whereas social play decreases. We proposed the hypothesis that both social grooming and social play in juveniles strengthen their social bonds in daily activities. We carried out field research on the social relationships among juvenile wild Japanese macaques in a troop in Kinkazan, Miyagi Prefecture, Japan, from fall 2007 to spring 2008 to investigate this hypothesis.Weevaluated three relationships among juveniles, play indices (PI), grooming indices (GI), and 3-m-proximity indices (3mI) of each dyad (i.e., interacting pair), and compared these social networks based on the matrices of the indices. The play and grooming networks were correlated with the association network throughout the two research periods. The multiple network level measurements of the play network, but not the grooming network, resembled those of the association network. Using a causal step approach, we showed that social play and grooming interactions in fall seem to predict associations in the following spring, controlling for the PI and GI matrix in spring, respectively. Social play and grooming for each juvenile were negatively correlated. The results partially support our predictions; therefore, the hypothesis that the biological function of social play among immature Japanese macaques is to strengthen their social bonds in the near future and develop their social life appears to be correct. For juvenile macaques, social play, rather than grooming, functions as an important social mechanism to strengthen affiliative relationships

Social information use is common in a wide range of group-living animals, notably in humans. The role it plays in decision-making could be a key to understanding how social groups make collective decisions. The observation of road-crossing behaviours in the presence of other individuals is an ideal means to study the influence of social information on decision-making. This study investigated the influence of culture on social information used by pedestrians in a potentially dangerous scenario, namely road crossing. We scored the collective crossing of pedestrians at four locations in Nagoya (Japan) and three locations in Strasbourg (France). French pedestrians cross against the lights much more often (41.9%) than Japanese ones (2.1%). Individuals deciding to cross the road were strongly influenced by the behaviour and the presence of other pedestrians, especially in Japan, where a stronger conformism was noted. However, Japanese pedestrians were half as likely to be influenced by social information as their French counterparts when crossing at the red light, as they were more respectful of rules. Men show riskier behaviour than women (40.6% versus 25.7% of rule-breaking, respectively), deciding quickly and setting off earlier than women. Further related studies could help target specific preventive, culture-specific solutions for pedestrian safety.

Task specialization in social insects leads to striking intra-specific differences in behaviour, morphology, physiology and longevity, but the underlying mechanisms remain not yet fully understood. Adult colonies of black garden ants (Lasius niger) have a single queen fertilized by one or a small number of males. The inter-individual genetic variability is thus relatively low, making it easier to focus on the individual molecular differences linked to the division of labour. Mass spectrometry-based proteomics enabled us to highlight which biological functions create the difference between queens, foragers and nest-workers. The proteome of each caste reflected nicely their social role: e.g. reproduction for queens, pesticide resistance for foragers – that are the most exposed to environmental risk factors – and, interestingly, digestion for nest-workers, thus highlighting proteomic profiles differences even among workers. Furthermore, our exploratory approach suggests energy trade-off mechanisms – in connection with the theory of social immunity – that might explain the difference in longevity between queens and workers. This study brings evidence that proteomics is able to highlight the subtle mechanisms of molecular regulation induced by social organization., SCOPUS: ar.j, info:eu-repo/semantics/published

We thank Norscia and Palagi for their insightful commentary on our article ‘Scratch that itch: revisiting links between self-directed behaviour and parasitological, social and environmental factors in a free-ranging primate’ [1]. We welcome such discussion because we think, as the authors themselves point out at the end of their commentary, that research needs to continue in this area. In general, we agree that different stressors may act at different time frames in triggering self-directed behaviours. As rightly pointed out by Norscia and Palagi, our analysis did not take into account the different time frames that would allow for separating the effects of acute and chronic stressors on self-directed behaviours. At the level of a behavioural observation of 15 min, we instead investigated whether the occurrence of scratching and self-grooming was linked to various factors such as lice load, social activities, neighbours in proximity and environmental conditions, together and/or separately. Our study was correlational and we, therefore, avoided claims of causality, although we did address potential causal mechanisms in the discussion. That said, we would nonetheless like to respond to several points made by Norscia and Palagi. First, one of the main points of our study was to highlight biases in the investigation of certain research hypotheses, such as those involving self-directed behaviours. Studies in primatology have often, if perhaps inadvertently, assumed that the primary drivers of self-directed behaviour (SDB) are social, with parasite or abiotic factors being secondary. Norscia and Palagi nonetheless state that ‘(…) the association between self-directed behaviours, and particularly scratching, with social, environmental and parasitological factors can be considered as more than just a hypothesis. Once established that the different factors are not alternative and that their relationship with scratching has been demonstrated, it is worth focusing on the role that each factor can have in …

International audience; The individual-based model GrooFiWorld proposes a parsimonious theory explaining the complexbehaviour of macaque societies. It suggests that the socio-spatial structure of the group underlies the emergenceof complex behaviour. A spatial structure with dominants at the center and subordinates at the peripheryemerges due to aggression. This structure influences the distribution of social interactions: individuals interactmore with close-by partners and thus several behavioural patterns emerge. In GrooFiWorld, however, individualshave no preferential interactions; whereas in primates, individuals prefer interactions with ’friends’. Thedistribution of interactions, then, may be influenced by ’friendships’ rather than spatial structure. To studythis, here, we omitted space from the model and investigated the eects of ’friendships’ on the emergence ofsocial behaviour and network structure. Results show that ’friendships’ promote cooperation but fail to produceother patterns characteristic of macaques. This highlights the importance that spatial structure may havein structuring macaque societies.

Individual-based computer models show that simple heuristic governing individuals’ behavior may suffice to generate complex patterns of social behavior at the group level such as those observed in animal societies. ‘GrooFiWorld’ is an example of such kind of computer models. In this model, self-organization and simple behavioral rules generate complex patterns of social behavior like those described in tolerant and intolerant societies of macaques. Social complexity results from the socio-spatial structure of the group, the nature of which is, in turn, a side-effect of intensity of aggression. The model suggests that a similar mechanism may give rise to complex social structures in macaques. It is, however, unknown if the spatial structure of the model and that of macaques are indeed similar. Here we used social networks analysis as a proxy for spatial structure of the group. Our findings show that the social networks of the model share similar qualitative features with those of macaques. As group size increases, the density and the average individual eigenvector centrality decrease and the modularity and centralization of the network increase. In social networks emerging from simulations resembling intolerant societies the density is lower, the modularity and centralization are higher, and the individuals ranking higher in the dominance hierarchy are more central than in the social networks emerging from simulations resembling egalitarian societies. Given the qualitative similarity between the social networks of the model and that of empirical data, our results suggest that the spatial structure of macaques is similar to that of the model. It seems thus plausible that, as in the model, the spatial structure combined with simple behavioral rules plays a role in the emergence of complex social networks and complex social behavior in macaques.

Little penguins (Eudyptula minor) have one of the widest geographic distributions among penguins, exposing them to variable ecological constraints across their range, which in turn can affect their foraging behaviour. Presumably, behavioural flexibility exists to allow animals to adapt to prevailing environmental conditions throughout their foraging range. This study examined whether complexity in the temporal organization of foraging sequences corresponds to characteristics of the foraging area across four colonies geographically distributed along the entire species’ range. Complexity and fractal scaling in spatiotemporal patterns of foraging behaviour have been theoretically linked to foraging efficiency in heterogeneous environments. Using fractal time series methods (detrended fluctuation analysis), we found that foraging complexity along a stochastic–deterministic gradient was associated with bathymetry in local foraging areas; little penguins foraging in deeper waters produced more stochastic/less deterministic foraging sequences than those foraging in shallower waters. Corresponding data on fledging success suggest that little penguins foraging in deeper waters also experienced reduced reproductive success. A principal component analysis further showed that our fractal scaling index, which specifically measured the degree to which sequences are long-range dependent (a deterministic phenomenon), correlated positively with foraging efficiency (prey encounter per unit time) and negatively with foraging effort (total time underwater). Our statistical models showed that production of complex foraging sequences with high degrees of stochasticity appears to be energy intensive. However, we could not determine which strategy would have maximized foraging success, a variable we could not measure, under the conditions observed. We propose that increasing stochastic elements in foraging behaviour may be necessary under challenging environmental conditions, but it may not be sufficient to match fitness gains attained under more favourable conditions.

When moving in groups, social animals tend to follow a leader which successfully attracted them. Many variables are known to affect an individual’s propensity to act as a leader. Depending on their nature, these variables underlie two theoretical paradigms (i) ‘leadership according to social indifference’, characterised by differences in personality or sociability, or (ii) ‘leadership according to need’, characterised by differences in energetic requirements or information content. Currently, it is not clear under which circumstances each of the two paradigms plays a larger role. Here, we tried to understand these paradigms by observing collective movements in female mallards. Each of these mallards previously learned individually to associate one of four locations in a maze with food rewards. We then formed groups of various compositions (group size range: 2–5 individuals) with respect to personality, sociability, energetic requirements, motivation and information content. We found that groups remained cohesive, and that certain individuals were consistent leaders within and between trials. The order of entering the maze was mainly determined by energetic requirements. However, soon after entering the maze, the progression order changed. Then, more socially indifferent individuals took the lead and this new order remained constant until all individuals reached the final location, which was usually the one the leader had learned. In addition, we investigated the role of naïve individuals in group decision-making. In our setup, adding naïve individuals broke the leadership consistency between trials and increased fission events. Overall, our results show that the onset of collective movements may be driven by different mechanisms compared to the movement progression itself.

Interspecies sexual behaviour or 'reproductive interference' has been reported across a wide range of animal taxa. However, most of these occurrences were observed in phylogenetically close species and were mainly discussed in terms of their effect on fitness, hybridization and species survival. The few cases of heterospecific mating in distant species occurred between animals that were bred and maintained in captivity. Only one scientific study has reported this phenomenon, describing sexual harassment of king penguins by an Antarctic fur seal. This is the first article to report mating behaviour between a male Japanese macaque (Macaca fuscata yakui) and female sika deer (Cervus nippon yakushimae) on Yakushima Island, Japan. Although Japanese macaques are known to ride deer, this individual showed clearly sexual behaviour towards several female deer, some of which tried to escape whilst others accepted the mount. This male seems to belong to a group of peripheral males. Although this phenomenon may be explained as copulation learning, this is highly unlikely. The most realistic hypothesis would be that of mate deprivation, which states that males with limited access to females are more likely to display this behaviour. Whatever the cause for this event may be, the observation of highly unusual animal behaviour may be a key to understanding the evolution of heterospecific mating behaviour in the animal kingdom.

groupe Cigognes France; International audience; How the spatial expansion of a species changes at a human time scale is a process difficult to determine. We studied the dispersal pattern of the French white stork population, using a 21-year ringing/resighting dataset. We used the graph-theory to investigate the strength of links between 5 populations (NorthEast , NorthWest , Centre, West, and South) and to determine factors important for the birds' movements. Two clusters of populations were identified within the metapopulation, with most frequent movements of individuals between NorthEastern and Centre populations, and between NorthWestern and Western populations. Exchanges of individuals between populations were asymmetrical, where NorthEast -ern and NorthWestern populations provided more emigrants than they received immigrants. Neither the geographical distance between populations, nor the difference in densities influenced the number of individuals exchanging between populations. The graph-theory approach provides a dynamic view of individual movements within a metapopulation and might be useful for future population studies in the context of conservation.

International audience; The capacity to use information provided by others to guide behavior is a widespread phenomenon in animal societies. A standard paradigm to test if and/or how animals use and transfer social information is through social diffusion experiments, by which researchers observe how information spreads within a group, sometimes by seeding new behavior in the population. In this article, we review the context, methodologyand products of such social diffusion experiments. Our major focus is the transmission of information from an individual (or group thereof) to another, and the factors that can enhance or, more interestingly, inhibit it. We therefore also discuss reasons why social transmission sometimes does not occur despite being expected to. We span a full range of mechanisms and processes, from the nature of social information itself and the cognitive abilities of various species, to the idea of social competency and the constraints imposed by the social networks in which animals are embedded. We ultimately aim at a broad reflection on practical and theoretical issues arising when studying how social information spreads within animal groups.

International audience; Although there exist advantages to group-living in comparison to a solitary lifestyle, costs and gains of group-living may be unequally distributed among group members. Predation risk, vigilance levels and food intake may be unevenly distributed across group spatial geometry and certain within-group spatial positions may be more or less advantageous depending on the spatial distribution of these factors. In species characterized with dominance hierarchy, high-ranking individuals are commonly observed in advantageous spatial position. However, in complex social systems, individuals can develop affiliative relationships that may balance the effect of dominance relationships in individual’s spatial distribution. The objective of the present study is to investigate how the group spatial distribution of a semi-free ranging colony of Mandrills relates to its social organization. Using spatial observations in an area surrounding the feeding zone, we tested the three following hypothesis: (1) does dominance hierarchy explain being observed in proximity or far from a food patch? (2) Do affiliative associations also explain being observed in proximity or far from a food patch? (3) Do the differences in rank in the group hierarchy explain being co-observed in proximity of a food patch? Our results showed that high-ranking individuals were more observed in proximity of the feeding zone while low-ranking individuals were more observed at the boundaries of the observation area. Furthermore, we observed that affiliative relationships were also associated with individual spatial distributions and explain more of the total variance of the spatial distribution in comparison with dominance hierarchy. Finally, we found that individuals observed at a same moment in proximity of the feeding zone were more likely to be distant in the hierarchy while controlling for maternal kinship, age and sex similarity. This study brings some elements about how affiliative networks and dominance hierarchy are related to spatial positions in primates.

International audience; Social learning – the transmission of behaviors through observation or interaction with conspecifics – can be viewed as a decision-making process driven by interactions among individuals. Animal group structures change over time and interactions among individuals occur in particular orders that may be repeated following specific patterns, change in their nature, or disappear completely. Here we used a stochastic actor-oriented model built using the RSiena package in R to estimate individual behaviors and their changes through time, by analyzing the dynamic of the interaction network of the fruit fly Drosophila melanogaster during social learning experiments. In particular, we re-analyzed an experimental dataset where uninformed flies, left free to interact with informed ones, acquired and later used information about oviposition site choice obtained by social interactions. We estimated the degree to which the uninformed flies had successfully acquired the information carried by informed individuals using the proportion of eggs laid by uninformed flies on the medium their conspecifics had been trained to favor. Regardless of the degree of information acquisition measured in uninformed individuals, they always received and started interactions more frequently than informed ones did. However, information was efficiently transmitted (i.e. uninformed flies predominantly laid eggs on the same medium informed ones had learn to prefer) only when the difference in contacts sent between the two fly types was small. Interestingly, we found that the degree of reciprocation, the tendency of individuals to form mutual connections between each other, strongly affected oviposition site choice in uninformed flies. This work highlights the great potential of RSiena and its utility in the studies of interaction networks among non-human animals.

Lice are socially-transmitted ectoparasites. Transmission depends upon their host's degree of contact with conspecifics. While grooming facilitates ectoparasite transmission via body contact, it also constrains their spread through parasite removal. We investigated relations between parasite burden and sociality in female Japanese macaques following two opposing predictions: i) central females in contact/grooming networks harbour more lice, related to their numerous contacts; ii) central females harbour fewer lice, related to receiving more grooming. We estimated lice load non-invasively using the conspicuous louse egg-picking behaviour performed by macaques during grooming. We tested for covariation in several centrality measures and lice load, controlling for season, female reproductive state and dominance rank. Results show that the interaction between degree centrality (number of partners) and seasonality predicted lice load: females interacting with more partners had fewer lice than those interacting with fewer partners in winter and summer, whereas there was no relationship between lice load and centrality in spring and fall. This is counter to the prediction that increased contact leads to greater louse burden but fits the prediction that social grooming limits louse burden. Interactions between environmental seasonality and both parasite and host biology appeared to mediate the role of social processes in louse burden., SCOPUS: ar.j, info:eu-repo/semantics/published

International audience; The successful reintroduction and restocking of the European Bison demands a reliable knowledge of the biology of this species. Yet little is known to date about the European bison, and empirical data remains insufficient to set up a reliable plan ensuring the reintro-duction, maintenance and survival of populations in habitats that have been largely modified by human activity. Studies of the ecology, social behaviour and management of bison are therefore crucial to the conservation of this species and its cohabitation with humans. To meet these challenges, we focused on movement patterns and space use in a semi-free-ranging herd of European bison living in the Réserve Biologique des Monts-d'Azur (France). Bison spend over 80% of their time foraging and resting; foraging mainly occurs around the artificial feeding sites (i.e., hay racks) or in meadows. The time of day and the presence of snow have no influence on the time budget allocated to each activity. Animals, however, spend more time at the food racks in winter. Bison also spend most of their time in small groups of individuals, confirming the occurrence of both fission-fusion dynamics and sexual segregation in this species. Bison seem to follow a Lévy walk pattern of movement, which is probably related to the geographical distribution and size of food patches in the reserve. The conclusions of this study provide a better understanding of the sociality, life habits and habitat use of bison, and also describe how the provision of hay affects all these behaviours. These results could be useful in the development of tools to select the most suitable habitats for the reintroduction, management and conservation of bison populations.

International audience; Animals living in groups will profit most from sociality if they coordinate the timing and nature of their activities. Self-organizing mechanisms can underlie coordination in large animal groups such as insect colonies or fish schools, but to what degree these mechanisms operate in socially complex species that live in small stable groups is not well known. We therefore examined the collective departure of wild chacma baboons, Papio ursinus, from their sleeping sites. First, in line with previous observations, the departure process appeared to be coordinated through the cue of individuals 'moving off', with no role for specific vocal or visual signalling. Second, we employed network analyses to explore how interindividual relationships influenced departure patterns, and found that a local rule, to follow the movements of those baboons with whom they shared a close social affiliation, determined when the baboon group departed. Finally, using an agent-based model, we were able to simulate mathematically the observed patterns of collective movements based upon the emergent rule that we identified. Our study adds weight to the idea that social complexity does not necessitate cognitive complexity in the decisionmaking process, consistent with heuristic decision-making perspectives studied by cognitive psychologists and researchers studying self-organization in biological systems.

SUMMARYLiving 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.

International audience; 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.

Different hypotheses explain variation in the occurrence of self-directed behaviour such as scratching and self-grooming: a parasite hypothesis linked with ectoparasite load, an environmental hypothesis linked with seasonal conditions and a social hypothesis linked with social factors. These hypotheses are not mutually exclusive but are often considered separately. Here, we revisited these hypotheses together in female Japanese macaques ( Macaca fuscata fuscata ) of Kōjima islet, Japan. We input occurrences of scratching and self-grooming during focal observations in models combining parasitological (lice load), social (dominance rank, social grooming, aggression received and proximity), and environmental (rainfall, temperature and season) variables. Using an information-theory approach, we simultaneously compared the explanatory value of models against each other using variation in Akaike's information criterion and Akaike's weights. We found that evidence for models with lice load, with or without environmental–social parameters, was stronger than that for other models. In these models, scratching was positively associated with lice load and social grooming whereas self-grooming was negatively associated with lice load and positively associated with social grooming, dominance rank and number of female neighbours. This study indicates that the study animals scratch primarily because of an immune/stimulus itch, possibly triggered by ectoparasite bites/movements. It also confirms that self-grooming could act as a displacement activity in the case of social uncertainty. We advocate that biological hypotheses be more broadly considered even when investigating social processes, as one does not exclude the other.

International audience; Matrilineal kin groups are common in social mammals and often exhibit cooperative behaviors. Social interactions in such groups may have varying consequences on fitness depending on the number of kin present. We used social network analysis to study which factors (including individual spatial distribution, sex, age, and kinship) affected patterns of aggressive interactions in Columbian ground squirrels during the important breeding period of lactation. In addition, we studied how patterns of aggressive interactions affected female reproduction and fitness. Received aggressions lessened as ground squirrels aged, likely reflecting greater dominance in older individuals. Outwards aggression peaked at prime reproductive age, but decreased in older individuals. In females, outwards aggressiveness was positively related to energy allocated to reproduction and annual fitness, suggesting that highly aggressive females were either of high intrinsic quality or were able to defend high-quality territories. Finally, female–female aggression was primarily targeted toward non-kin individuals, revealing the advantage for breeding adult females of having close kin neighbors that were also breeding. Thus, breeding females that were close kin appeared to be “genial neighbors” that benefited from increased fitness, highlighting the role of kin selection in mitigating the costs (e.g., injuries, stress) of aggression.

Social network analysis is a powerful tool that enables us to describe and quantify relationships between individuals. So far most of the studies rely on the analyses of various network snapshots, but do not capture changes over time. Here we use a stochastic actor-oriented model (SAOM) to test both the structure and the dynamics of relationships of three groups of wild vervet monkeys. We found that triadic closure (i.e., the friend of a friend is a friend) was significant in all three groups while degree popularity (i.e., the willingness to associate with individuals with high degree of connections) was significant in only two groups (AK, BD). The structure and dynamics of relationships according to the attributes of sex, matrilineand age differed significantly among groups. With respect to the structure, when analyzing the likelihood of bonds according to the different attributes, we found that individuals associate themselves preferably to individuals of the same sex only in two groups (AK, NH), while significant results for attachment to individuals of the same matriline were found also in two groups (BD, NH). With respect to the dynamics, i.e., how quickly relationships are modified, we found in two groups (AK, BD) that females' relationships were more prone to variation than males.' In the BD group, relationships within high-ranking matrilines were less stable than low-ranking ones while in the NH group, juveniles' relationships were also less stable than adults' ones. The intergroup variation indicates that establishing species-specific or even population specific characteristics of social networks for later between-species comparisons will be challenging. Although, such variation could also indicate some methodological issue, we are quite confident that data was collected similarly within the different groups. Our study therefore provides a potential new method to quantify social complexity according to natural demographic variation.

International audience; While many studies focus on how animals use public information, the dynamics of information spread and maintenance within groups, i.e. the ‘ecology of information’, have received little attention. Here we use fruitflies trained to lay eggs on specific substrates to implement information into groups containing both trained and untrained individuals. We quantify inter-individual interactions and then measure the spread of oviposition preference with behavioural tests. Untrained individuals increase their interactive approaches in the presence of trained individuals, and the oviposition preference transmission is directly proportional to how much trained and untrained individuals interact. Unexpectedly, the preference of trained individuals to their trained oviposition substrate decreases after interactions with untrained individuals, leading to an overall informational loss. This shows that social learning alone is not enough to support informational stability.

International audience; In order to maximize their fitness, animals have to deal with different environmental and social factors that affect their everyday life. Although the way an animal behaves might enhance its fitness or survival in regard to one factor, it could compromise them regarding another. In the domain of decision sciences, research concerning decision making focuses on performances at the individual level but also at the collective one. However, between individual and collective decision making, different terms are used resulting in little or no connection between both research areas. In this paper, we reviewed how different branches of decision sciences study the same concept, mainly called speed-accuracy trade-off, and how the different results are on the same track in terms of showing the optimality of decisions. Whatever the level, individual or collective, each decision might be defined with three parameters: time or delay to decide, risk and accuracy. We strongly believe that more progress would be possible in this domain of research if these different branches were better linked, with an exchange of their results and theories. A growing amount of literature describes economics in humans and eco-ethology in birds making compromises between starvation, predation and reproduction. Numerous studies have been carried out on social cognition in primates but also birds and carnivores, and other publications describe market or reciprocal exchanges of commodities. We therefore hope that this paper will lead these different areas to a common decision science.

International audience; Group membersmust decide collectively when and where to go despite their different nutrient requirements. One mechanism underlying consensus decisions is the proposition by one individual to move. The individual frequently initiating movements is often named a "leader", and this individual may be the most dominant, the oldest or may have the greatest physiological needs. However, high-ranking individuals are often those with the highest body mass, and thus the highest nutrient requirements. In this study, we use a state-dependent model to assess the importance of dominance and nutrient requirements to the initiation of group movements, testing different combinations of effects of these interacting factors. We first show using a theoretical approach that whatever the correlation between the dominance hierarchy and body mass, all decision-making systems are viable (or stable). However, in most cases, one individual does become the leader, and nutrient requirements appear to be more important for determining which individual will emerge as the leader than pre-existing individual characteristics such as their dominance rank. We obtained the same result when we compared the simulated distributions of initiations to the observed distributions in three macaque species. Results of our comparison of three macaque groups suggest that we can predict which group member will be the leader simply by knowing its body mass and its reproductive state. Understanding the link between dominance, needs and leadership may be a key to understanding consensus decisions and collective motion in animal groups, and might provide insight into the management of animal groups and their conservation.

International audience; The difficulty involved in following mandrills in the wild means that very little is known about social structure in this species. Most studies initially considered mandrill groups to be an aggregation of one-male/multifemale units, with males occupying central positions in a structure similar to those observed in the majority of baboon species. However, a recent study hypothesized that mandrills form stable groups with only two or three permanent males, and that females occupy more central positions than males within these groups. We used social network analysis methods to examine how a semi-free ranging group of 19 mandrills is structured. We recorded all dyads of individuals that were in contact as a measure of association. The betweenness and the eigenvector centrality for each individual were calculated and correlated to kinship, age and dominance. Finally, we performed a resilience analysis by simulating the removal of individuals displaying the highest betweenness and eigenvector centrality values. We found that related dyads were more frequently associated than unrelated dyads. Moreover, our results showed that the cumulative distribution of individual betweenness and eigenvector centrality followed a power function, which is characteristic of scale-free networks. This property showed that some group members, mostly females, occupied a highly central position. Finally, the resilience analysis showed that the removal of the two most central females split the network into small subgroups and increased the network diameter. Critically, this study confirms that females appear to occupy more central positions than males in mandrill groups. Consequently, these females appear to be crucial for group cohesion and probably play a pivotal role in this species.