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THTHESEESE`` En vue de l’obtention du DOCTORAT DE L’UNIVERSITE´ DE TOULOUSE D´elivr´e par : l’Universit´eToulouse 3 Paul Sabatier (UT3 Paul Sabatier) Cotutelle internationale University of Groningen Pr´esent´ee et soutenue le mardi 5 d´ecembre 2017 (05/12/2017) par : Valentin Lecheval Experimental analysis and modelling of the behavioural interactions underlying the coordination of collective motion and the propagation of information in fish schools JURY Nicolas Destainville Professeur Pr´esident du Jury Simon Verhulst Professeur MembreduJury Rineke Verbrugge Professeur MembreduJury Jose´ Halloy Professeur Rapporteur Christos C. Ioannou Docteur Rapporteur Colin J. Torney Docteur Rapporteur Ecole´ doctorale et sp´ecialit´e : SEVAB : Ecologie,´ biodiversit´eet ´evolution Unit´e de Recherche : Centre de Recherches sur la Cognition Animale (UMR 5169) Directeur(s) de Th`ese : Charlotte K. Hemelrijk et Guy Theraulaz Rapporteurs : Jos´eHalloy, Christos C. Ioannou et Colin J. Torney 2 Acknowledgements The research presented in this thesis is the result of a collective effort that has emerged from interactions between many individuals to whom I am extremely grateful. First, I would like to warmly thank Guy Theraulaz and Charlotte Hemelrijk. They have initiated a fruitful collaboration between two research teams in Toulouse and Groningen, that investigate moving animal groups with different approaches and methods. I am very pleased for having been part of this project during three years, under their demanding and enriching supervision. I would also like to thank Cl´ement Sire for all the work he dedicated to this thesis and for his inspired and illuminating assistance regarding analysis and modelling. Thank you to all members of the research teams involved in this work, that is staff, researchers, students and friends of the Centre de Recherches sur la Cognition Animale (in particular the CAB1 and IVEP2 teams) in Toulouse as well as the BPE3 and TRESˆ 4 teams in Groningen. As for the technical support, I would like to stress and thank the very important contributions of Hanno Hildenbrandt, Patrick Arrufat, St´ephane Ferrere, Mathieu Moreau, Maud Combe and G´erard Latil who made all sorts of ideas possible. Thank you to the two master students who have been working with us in Toulouse, Pierre Tichit, Marlene Afflerbach and Alexandra Litchinko. Their dedication to this project has been amazing and their contribution substantial. I would also like to thank Jean-Baptiste Ferdy and Christophe Eloy for their time, ideas and inputs to this work, during my annual PhD committee. Thank you also to Li Jiang and Emanuele Crosato and their respective teams for their very interesting studies based on the empirical work of this thesis as well as for their friendship, that was of main importance during the talks we all gave for the first time in congresses. The teaching dimension of my position as a PhD student is unfortunately missing from this thesis, but I would like to thank the 1000 students I have had over three years of what became an ∼ intensive and inspiring teaching duty, masterfully assisted by Sergine Ponsard and La¨etitia Buisson. Finally, I would like to thank Jacques Gautrais, Richard Fournier, St´ephane Blanco and Ana¨ıs Khuong for their supervision of my first research project, a few years ago. They have not only initiated my interests in collective behaviours and in modelling but also have deeply shaped my research and teaching practises. 1Collective Animal Behaviour 2Interindividual Variability and Emergent Plasticity 3Behavioural and Physiological Ecology 4Theoretical Research in Evolutionary Λife Sciences i ii Summary Collective motion is ubiquitous in fish. Large groups may comprise thousands to millions of indi- viduals. However, it is not yet understood what are the local interaction rules that underlie these collective patterns. In this thesis, we investigate in a small gregarious fish, the rummy-nose tetra (Hemigrammus rhodostomus), the mechanisms underlying both the coordination of motion and the propagation of information in their schools. To discover the connection between individual behaviour and patterns at the collective level, we follow an approach that tightly combines experiments and modelling. The first part of the thesis is dedicated to the behavioural mechanisms underlying the coor- dinated swimming in these schools. For this, we analysed the motion of a single individual and pairs of individuals swimming freely in a circular arena. H. rhodostomus has a burst-and-coast swimming style. This consists of sudden changes of heading combined with brief accelerations fol- lowed by quasi-passive, straight decelerations. We segmented their trajectories on the basis of this intermittent swimming mode. This segmentation determined the analysis of experimental data and the design of the model. We developed a new method to measure and disentangle the interactions between a fish and the wall and between pairs of fish. We tested these findings with a model derived from physical analogies and symmetry considerations. Our results support the presence of interactions among fish based on the coexistence of attraction and alignment. We also investigated for fish swimming in a ring-shaped tank how an individual integrates the information coming from several other fish and from obstacles in its neighbourhood. For this, we develop a computational model based on maps of behavioural actions that were extracted from empirical data. We tested in this model whether the properties of schools at the global-level were reproduced when fish reacted only to the strongest stimulus they perceived. We rejected this for observations in groups of 5 fish. The second part of the thesis is dedicated to the analysis of the propagation of information in reaction to internal and external perturbations, in schools of H. rhodostomus. The internal perturbations concern spontaneous collective U-turns occurring in a ring-shaped tank. The global properties of the propagation came from empirical data of group sizes with 1 to 20 fish. We formulate an Ising-spin model that integrates both asymmetrical interactions among fish and the tendency of individuals to follow the majority of their neighbours. The model shows that local social conformity may be underlying both the dynamics observed during the collective U-turns and the sharp decrease of the frequency of collective U-turns as the size of the group increases. Finally, we develop a preliminary experimental method to induce controlled external pertur- bations with the objective to investigate the propagation of information during disturbances. We show that aversive conditioning (i) can be performed in this species, (ii) triggers collective escape reactions and (iii) transfers from the training condition to a new experimental set-up. These re- sults come from a training in which a green light elicits an escape reaction in conditioned fish. Our findings suggest that the proportion of conditioned individuals in a group is critical in triggering collective escape reactions. iii iv R´esum´e Les d´eplacements collectifs sont omnipr´esents chez les poissons et peuvent comprendre des groupes de plusieurs milliers ou millions d’individus. Cependant, les interactions locales et les r`egles com- portementales individuelles `al’origine de ces comportements collectifs posent encore question. Dans cette th`ese, nous ´etudions les m´ecanismes sous-jacents `a la coordination du d´eplacement et `ala propagation de l’information dans les bancs d’un petit poisson gr´egaire, le nez rouge (Hem- igrammus rhodostomus). L’approche de cette th`ese repose sur une ´etroite combinaison entre les m´ethodes exp´erimentales et de mod´elisation dans l’objectif de d´ecouvrir les liens entre les com- portements individuels et les motifs observ´es `al’´echelle collective. La premi`ere partie du manuscrit est d´edi´ee aux m´ecanismes comportementaux qui sous-tendent la coordination de la nage en banc chez H. rhodostomus. Nous y analysons le d´eplacement d’un individu solitaire ou d’une paire de poissons nageant librement dans une ar`ene circulaire. H. rhodos- tomus a un comportement de nage intermittente. Ce mode de nage est constitu´ede changements de direction soudains combin´es `ade br`eves saccades natatoires suivies d’une phase d’accostage durant laquelle le corps du poisson reste rigide. L’analyse des donn´ees exp´erimentales ainsi que le travail de mod´elisation reposent sur la segmentation des trajectoires des poissons sur la base du comporte- ment de nage intermittente. Nous avons d´evelopp´eune nouvelle m´ethode pour mesurer et isoler les interactions d’un poisson avec un mur ou entre deux poissons. Ces mesures sont test´ees `al’aide d’un mod`ele inspir´epar des consid´erations de physique et de sym´etrie. Nos r´esultats soutiennent la pr´esence d’interactions reposant sur la coexistence d’attraction et d’alignement. Nous ´etudions aussi comment les individus int`egrent l’information issue de plusieurs cong´en`eres et d’obstacles dans leur voisinage. Nous formulons un mod`ele computationnel qui repose sur des cartes d’actions comportementales extraites des donn´ees exp´erimentales. Nous testons l’hypoth`ese selon laquelle les poissons r´eagissent uniquement au stimulus le plus important qu’ils per¸coivent, en v´erifiant que l’hypoth`ese permet de reproduire les propri´et´es du banc `al’´echelle collective. Nous concluons que cette hypoth`ese n’est pas suffisante pour reproduire les caract´eristiques de bancs form´es dans des exp´eriences r´eunissant 5 poissons dans un dispositif annulaire. La seconde partie du manuscrit est d´edi´ee `al’analyse de la propagation d’information dans les bancs de H. rhodostomus, en r´eaction `ades perturbations internes ou externes. Nous analysons la propagation de l’information en r´eponse `ades perturbations internes se produisant lors de demi-tours collectifs spontan´es observ´es dans un dispositif annulaire, avec des groupes allant de 1 `a20 poissons.

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