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info:eu-repo/semantics/nonPublished

info:eu-repo/semantics/published

info:eu-repo/semantics/published

info:eu-repo/semantics/published

info:eu-repo/semantics/published

info:eu-repo/semantics/published

Many studies on collective animal behavior seek to identify the individual rules that underlie collective patterns. However, it was not until the recent advancements of micro-electronic and embedded systems that scientists were able to create mixed groups of sensor-rich robots and animals and study collective interactions from the within a bio-hybrid group. In recent work, scientists showed that a robot-controlled lure is capable of influencing the collective decisions of zebrafish Danio rerio shoals moving in a ring and a two-room setup. Here, we study a closely related topic, that is, the collective behavior patterns that emerge when different behavioral models are reproduced through the use of a robotic lure. We design a behavioral model that alternates between obeying and disobeying the collective motion decisions in order to become socially accepted by the shoal members. Subsequently, we compare it against two extreme cases: a reactive and an imposing decision model. For this, we use spatial, directional and information theoretic metrics to measure the degree of integration of the robotic agent. We show that our model leads to similar information flow as in freely roaming shoals of zebrafish and exhibits leadership skills more often than the open-loop models. Thus, in order for the robot to achieve higher degrees of integration in the zebrafish shoal, it must, like any other shoal member, be bidirectionally involved in the decision making process. These findings provide insight on the ability to form mixed societies of animals and robots and yield promising results on the degree to which a robot can influence the collective decision making., SCOPUS: ar.j, info:eu-repo/semantics/published

Collective motion in fish shoals have been studied for many years. Multiple shoal structures and configurations have been observed and indexed since the early 20th century. In the last decades, the development of tracking techniques allowed precise measurements of the shoal dynamics. Nevertheless, most of the studies based on those measurements mainly focus on few configurations (usually an organized and mobile configuration named school and a disorganized and static one named swarm) and do not integrate the variety of structures a shoal can adopt. Moreover, their discrimination methods for these configurations are not adapt to an accurate study of the alternation dynamics between these.Fish shoals take many advantage of the heterogeneities found in their environment (shelters, visual cues, meeting points. ). These heterogeneities can largely influence the shoal dynamics. Among these, the floating objects are the most studied due to economic issues related to the use of FADs (fish aggregating devices) in fishery. Nevertheless, only sparse data are collected in the field as many technical challenges has to be be tackled. The lack of precise measurements makes difficult to study the shoal dynamics under and around floating objects. Similar mechanisms can underlie the floating objects association of many fish species. Furthermore, small species in laboratory experiments associate with floating objects as well. This thesis presents a study of the influence of the floating objects and the population size on the shoal dynamics. In this way, a set of laboratory experiments has been conducted on zebrafish (Danio rerio) varying the number of individuals (from 5 to 25) and the number of floating objects (from 0 to 2). A tracking technique has been developed to detect the fishes under the objects and rebuild fish trajectories when one fish hides others. A thorough analysis of shoal measurements (alignment, speed, ) allowed to establish a discrimination methodology of multiple, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

info:eu-repo/semantics/nonPublished

info:eu-repo/semantics/published

info:eu-repo/semantics/nonPublished

info:eu-repo/semantics/published

info:eu-repo/semantics/nonPublished

info:eu-repo/semantics/nonPublished

info:eu-repo/semantics/nonPublished

Collective behaviour models can predict behaviours of schools, flocks, and herds. However, in many cases, these models make biologically unrealistic assumptions in terms of the sensory capabilities of the organism, which are applied across different species. We explored how sensitive collective behaviour models are to these sensory assumptions. Specifically, we used parameters reflecting the visual coverage and visual acuity that determine the spatial range over which an individual can detect and interact with conspecifics. Using metric and topological collective behaviour models, we compared the classic sensory parameters, typically used to model birds and fish, with a set of realistic sensory parameters obtained through physiological measurements. Compared with the classic sensory assumptions, the realistic assumptions increased perceptual ranges, which led to fewer groups and larger group sizes in all species, and higher polarity values and slightly shorter neighbour distances in the fish species. Overall, classic visual sensory assumptions are not representative of many species showing collective behaviour and constrain unrealistically their perceptual ranges. More importantly, caution must be exercised when empirically testing the predictions of these models in terms of choosing the model species, making realistic predictions, and interpreting the results., info:eu-repo/semantics/published

In this work, we address the case of red nose tetra fish Hemigrammus bleheri swimming in groups in a uniform flow, giving special attention to the basic interactions and cooperative swimming of a single pair of fish. We first bring evidence of synchronization of the two fish, where the swimming modes are dominated by ‘out-phase’ and ‘in-phase’ configurations. We show that the transition to this synchronization state is correlated with the swimming speed (i.e. the flow rate), and thus with the magnitude of the hydrodynamic pressure generated by the fish body during each swimming cycle. From a careful spatio-temporal analysis corresponding to those synchronized modes, we characterize the distances between the two individuals in a pair in the basic schooling pattern. We test the conclusions of the analysis of fish pairs with a second set of experiments using groups of three fish. By identifying the typical spatial configurations, we explain how the nearest neighbour interactions constitute the building blocks of collective fish swimming., info:eu-repo/semantics/published

Collective motion is one of the most ubiquitous behaviours displayed by social organisms and has led to the development of numerous models. Recent advances in the understanding of sensory system and information processing by animals impels one to revise classical assumptions made in decisional algorithms. In this context, we present a model describing the three-dimensional visual sensory system of fish that adjust their trajectory according to their perception field. Furthermore, we introduce a stochastic process based on a probability distribution function to move in targeted directions rather than on a summation of influential vectors as is classically assumed by most models. In parallel, we present experimental results of zebrafish (alone or in group of 10) swimming in both homogeneous and heterogeneous environments. We use these experimental data to set the parameter values of our model and show that this perception-based approach can simulate the collective motion of species showing cohesive behaviour in heterogeneous environments. Finally, we discuss the advances of this multilayer model and its possible outcomes in biological, physical and robotic sciences., info:eu-repo/semantics/published

In social species, food exploitation is a challenging cooperative task that requires communication and coordination with some individuals that are more influential in the final foraging process. Among recruiters of the ant Tetramorium caespitum that have discovered food, some individuals act as leaders that physically guide groups of recruits until they reach the food source. Here, we discovered that highly motivated recruiters that focus their recruiting activity on areas close to the nest entrance and that perform a high number of contacts with nestmates in a short period of time are more likely to lead a group of followers on their next foraging trip. Based on the individual tracking of recruiters, we also show that the probability to lead a group is homogeneously distributed and that no specialisation into leadership occurs even over successive foraging trips. Instead of a permanent leadership, a distributed leadership that is mainly based on the motivation level of recruiters appears as an efficient way to process information and make collective decisions. Finally, we discuss how heterogeneity among group members in their access to information, their motivation to recruit or the social context of recruitment can be coupled to self-organising processes and can ultimately lead to adaptive collective patterns., SCOPUS: ar.j, info:eu-repo/semantics/published

In the ant species Tetramorium caespitum, collective foraging relies on group mass communication in which successful scouts lay a recruitment trail but also guide a group of nestmates to the food source. We conducted experiments to understand how group leaders may improve the success of recruits in reaching the food source and whether they adjust their leading behaviour to their audience, that is, to the following response of recruits along the foraging journey. We characterized the trajectories of leaders by measuring their straightness, angular deviation, maximal amplitude and walking speed. Trajectometric values highlighted that a straight path coupled with a slow walking speed increased the probability of followers reaching the food whereas leaders that walked at higher speed and deviated far from the food-nest beeline were more likely to lose recruits. Leaders did not seem to heed their audience since they did not reduce their speed or their path sinuosity after the loss of a recruit along their outbound journey. Information transfer about food resources by T.caespitum leaders is thus targeted towards a restricted number of recruits but without the informed individuals exerting any control over the following response of their audience. We discuss strengths and weaknesses of group recruitment compared with simpler or more sophisticated forms of information sharing and we debate the status of group recruiters regarding the concept of leadership in animal groups. © 2014 The Association for the Study of Animal Behaviour., SCOPUS: ar.j, info:eu-repo/semantics/published

L’exploitation collective de ressources par les sociétés animales repose sur la coopération et la coordination des membres du groupe. Selon la structure sociale des espèces envisagées, leurs comportements collectifs seront dictés par quelques individus imposant leurs choix ou au contraire impliqueront tous les membres du groupe. Chez la fourmi Tetramorium caespitum, la récolte de nourriture repose à la fois sur le dépôt d’une piste de phéromone chimique commune lors du retour des ouvrières vers le nid et sur le recrutement de groupe de congénères guidés par des individus leaders jusqu’à la source de nourriture. Cette espèce nous donne donc l’opportunité d’étudier un système de recrutement couplant des mécanismes décentralisés à la présence d’individus leaders.Nos observations montrent que le recrutement de groupe est lié à une forte motivation de certaines ouvrières à exploiter une source de nourriture découverte. Lorsqu’elles recrutent un groupe, elles passent peu de temps à l’intérieur du nid mais effectuent un taux élevé de contacts avec leurs congénères, principalement à l’entrée du nid, avant de repartir en direction de la nourriture, suivie par le peloton de fourrageuses. Durant le trajet, si une trajectoire rectiligne et une faible vitesse de déplacement favorisent la probabilité des recrutées d’atteindre la source, la perte de recrutées n’entraîne cependant aucune modification du comportement de la meneuse. Enfin, un suivi individualisé des fourrageuses au cours du recrutement montre que la probabilité d’être observée en tant que leader est répartie de manière homogène entre les individus découvrant la source de nourriture, sans influence du nombre de trajets qu’elles ont déjà effectués.Par ailleurs, nous avons étudié l’influence des leaders sur les choix collectifs de la colonie. Les leaders modulent les caractéristiques du recrutement -­-fréquence des groupes, tailles des groupes-­- en fonction des caractéristiques de la source exploitée. Grâce à un, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

For collective decisions to be made, the information acquired by experienced individuals about resources' location has to be shared with naïve individuals through recruitment. Here, we investigate the properties of collective responses arising from a leader-based recruitment and a self-organized communication by chemical trails. We develop a generalized model based on biological data drawn from Tetramorium caespitum ant species of which collective foraging relies on the coupling of group leading and trail recruitment. We show that for leader-based recruitment, small groups of recruits have to be guided in a very efficient way to allow a collective exploitation of food while large group requires less attention from their leader. In the case of self-organized recruitment through a chemical trail, a critical value of trail amount has to be laid per forager in order to launch collective food exploitation. Thereafter, ants can maintain collective foraging by emitting signal intensity below this threshold. Finally, we demonstrate how the coupling of both recruitment mechanisms may benefit to collectively foraging species. These theoretical results are then compared with experimental data from recruitment by T. caespitum ant colonies performing group-mass recruitment towards a single food source. We evidence the key role of leaders as initiators and catalysts of recruitment before this leader-based process is overtaken by self-organised communication through trails. This model brings new insights as well as a theoretical background to empirical studies about cooperative foraging in group-living species. © 2012 Elsevier Ltd., SCOPUS: ar.j, info:eu-repo/semantics/published