Catégorie d'événements: PhD defense

Célia BAK – PhD defense

Defense in french

Team : REMEMBeR (Revealing Memory Mechanisms of the Brain) – CRCA-CBI

Supervisors : Cédrick FLORIAN (CRCA-CBI) et Claire RAMPON (CRCA-CBI)

Committee members :

  • Anne-Laurence BOUTILLIER – Laboratoire de Neurosciences Cognitives et Adaptatives (LNCA), Strasbourg
  • Cyrille VAILLEND – Institut des Neurosciences Paris-Saclay (NeuroPsi), Paris
  • Jean-Louis GUILLOU – Institut de Neurosciences Cognitives et Intégratives d’Aquitaine (INCIA), Bordeaux
  • Shauna PARKES – Institut de Neurosciences Cognitives et Intégratives d’Aquitaine (INCIA), Bordeaux
  • Guillaume ISABEL – Centre de Recherches sur le Cognition Animale (CRCA-CBI), Toulouse

Abstract :

The long term memory is formed through a consolidation process requiring de novo gene transcription, regulated by epigenetic mechanisms. Epigenetic modifications, including histone acetylations that structure chromatin, are added or removed respectively by histone acetyltransferases (HATs) and histone deacetylases (HDACs). The latter are recruited to targeted genes by transcriptional repressor complexes. Although still understudied, the literature shows the involvement of these repressor complexes in the formation of different types of memory, thus highlighting the question of their significant implication in mnemonic processes. Therefore, we chose to study one of these complexes, SIN3A- HDACs, in the context of hippocampus-dependent memory consolidation. Furthermore, numerous studies have investigated the function of HDACs, especially HDACs 1 and 2, in memory processes using genetically modified mice models for these enzymes. However, their role in the memory consolidation phase can only be demonstrated by their punctual inhibition, such as through acute administration of pharmacological HDAC inhibitors. Thus, to test our hypothesis that the SIN3A-HDAC complex participates in long term memory formation, we specifically targeted the two entities of this complex by attempting to establish a SIN3A-depleted mouse model or by specifically inhibiting HDACs 1 and 2 through the administration of Compound 60 (Cpd-60) in the dorsal hippocampus. The first results of this thesis work showed a role for SIN3A, but no effect of the Cpd-60 on the consolidation of contextual memory generated by subjecting adult mice to fear conditioning. The first part of this manuscript therefore presents the different approaches we used to target SIN3A and the effects of Cpd-60 injection at the molecular and behavioral levels. The second part of this thesis work addresses the effect of age on the behavioral and brain response of mice to a looming stimulus, mimicking the rapid approach of a flying predator. Adaptive defensive behaviors are essential for species survival. While these behaviors begin to develop early in an individual’s life, there is still little knowledge about how they evolve in older individuals. Considering that aging is accompanied by a decline in cognitive and physical functions, we hypothesize that innate fear behaviors and underlying brain mechanisms may undergo modifications with age. This work thus examines this hypothesis by observing the reaction of old mice to a threatening visual stimulus compared to young ones. Our results show that aged mice exhibit a different fear response than younger mice when confronted with the looming stimulus. Unlike young mice, old mice tend to adopt a freezing behavior without seeking for a refuge. Interestingly, this altered behavioral response in aged mice is associated with a distinct pattern of brain functional connectivity compared to young mice, with a deficit in cellular activation in key brain structures that regulate innate fear behaviors.

Djamaa ATAMENA – PhD defense

Defense in french

Team : MItochondria- & ExperieNce- Dependent neuronal plastIcity, NeurodeGeneration (MINDING), CRCA-CBI

Supervisor : Pr. Pascale BELENGUER (CRCA-CBI)

Committee members :

  • Dr. CORRAL-DEBRINSKI Marisol, Rapporteure
  • Pr. BLONDEL Marc, Rapporteur
  • Dr. DUNIA Daniel, Examinateur
  • Pr. BELENGUER Pascale, Directrice de thèse

Abstract :

Hereditary optic neuropathies (HON), leading to severely impaired vision, are due to the degeneration of the Retinal Ganglion Cells (RCG) whose axons form the optic nerve. One of the most common HON encountered in clinics is Dominant Optic Atrophy (DOA). DOA is mainly caused by mutations of the gene coding the mitochondrial protein OPA1. OPA1 is involved in mitochondrial fusion a mechanism that controls, together with mitochondrial fission, the morphology and the functions of mitochondria. Clinical manifestations include progressive bilateral and symmetrical vision loss beginning from early childhood. In up to 20% of cases, extra-ocular manifestations are also reported leading to syndromic forms of DOA (sensorineural deafness, ataxia, peripheral neuropathy …). The disease is marked by a highly variable inter- and intra-familial expressivity, from patients being asymptomatic, to some totally blind or suffering from multisystemic affections. Altogether, this suggests the presence of genetic and/or environmental factors that confer, along with the primary mutation, a strong influence on the disease manifestation. So far, no modifying factors that could modulate DOA expressivity have been clearly identified. To investigate the influence of genetic modifying factors on DOA expressivity, we used a previously described DOA mouse model bearing the c.1065+5G→A Opa1 mutation which we switched from the mixed C3H;C57BL/6J to pure C57BL/6J genetic background. The phenotypic consequences on the pure genetic background was less severe, without any sign of RGC and axonal degeneration, supporting the contribution of genetic secondary factors to the phenotypic variability in DOA. However, we described a negative effect on RGC connectivity suggesting that OPA1 deficiency may first impair RGC functioning through early synaptic defects and eventually lead to neuronal degeneration. This opens a way to new clinical considerations for early diagnosis together with a new therapeutic window before neurodegeneration. Currently, there is no curative treatment for DOA and innovative therapeutic solutions are still awaited. We aimed at establishing the proof of concept for two novel therapeutic approaches based on their abilities to rescue the consequences of OPA1-deficiency. The first approach aims to evaluate the effects of a neuroprotective protein, the Bornavirus X protein. Our team showed that the expression of this protein in primary cultured neurons restores the mitochondrial and neuronal defects associated with OPA1 deficiency, so I set up a preclinical trial using another DOA mouse model. For that purpose, adeno-associated viruses expressing the X protein were injected into the retina of 3-months-old mice, before the onset of the first symptoms. The consequences of the X protein expression on the alterations of the visual function as well as on RGC and optic nerve degeneration will be soon analyzed after 11 months of treatment. The second pharmacological approach is based on the repositioning of FDA-approved molecules, Hexestrol and Clomiphene. Our team showed that these molecules prevent the lethality, the mtDNA loss and the mitochondrial fragmentation induced by inactivation of the OPA1 homologue in yeast, Msp1p. I pursued this study evaluating the effect of these molecules in mammalian DOA model cells ie fibroblasts of OPA1 mutated patients and OPA1-deficient rat cortical neurons. In both models, we showed that both molecules rescued mitochondrial morphology defects by inhibiting mitochondrial fission. Further investigations are currently performed to address their effect on dendritic arborization and synapses in neurons. The encouraging results that I obtained make these two therapeutic strategies good candidates to treat DOA by focusing on the correction of the defects rather than the mutation itself. They could be thus applied to other mitochondrial HON as well as mitochondrial-related neurodegenerative diseases.

Thomas BASSANETTI – PhD defense

Defense in french

Team : Collective animal behaviour (CAB), CRCA-CBI

Supervisors : Guy THERAULAZ (CRCA-CBI) & Clément SIRE (LPT)

Committee members :Modifier cette traduction en Français

  • Laeticia Gauvin, Directrice de Recherches à l’IRD, Aubervilliers, France (Rapporteure)
  • David Chavalarias, Directeur de Recherches au CNRS, Institut des Systèmes Complexes de Paris Île-de-France, France (Rapporteur)
  • Alain Barrat, Directeur de recherches au CNRS, Centre de Physique Théorique, Marseille, France (Examinateur)
  • Umberto Grandi, Professeur, Université Toulouse Capitole, Toulouse, France (Examinateur)
  • Clément Sire, CNRS, Directeur de Recherches au CNRS, Université Toulouse Paul Sabatier, France (Co-directeur de thèse)
  • Guy Theraulaz, CNRS, Directeur de Recherches au CNRS, Université Toulouse Paul Sabatier, France (Co-directeur de thèse)

Abstract :

Stigmergy is a generic coordination mechanism widely used by animal societies, in which traces left by individuals in the environment guide and stimulate the subsequent actions of the same or different individuals. In the human context, with the digitization of society, new forms of stigmergic processes have emerged through the development of online services that extensively exploit the digital traces left by their users, in particular, using rating-based recommendation systems. Therefore, understanding the impact of these digital traces on both individual and collective decision-making is essential.

This study pursues two main objectives. First, I investigate and develop a model of the interactions of groups of individuals with their digital traces, and determine how they can exploit these traces to cooperate in an information search task. Subsequently, the research explores the impact of intragroup and intergroup competition on the dynamics of cooperation in the framework of this information search task.

To answer these questions, we have developed the online multiplayer Stigmer game, on which we base 16 series of experiments under varying conditions. In this game, groups of individuals leave and exploit digital traces in an information search task that implements a 5-star rating system. This system is similar to recommendation systems used by many online marketplaces and platforms, where users can evaluate products, services, or sellers. In the game, all individuals interact with a grid of hidden values, searching for cells with the highest values, and using only indirect information provided in the form of colored traces resulting from their collective ratings. This controlled environment allows for a thorough and quantitative analysis of individual and collective behaviors, and offers the possibility of manipulating and studying the combined impact of intragroup and intergroup competition on cooperation.

The experimental and modeling results indicate that the type and intensity of competition determine how individuals interpret and use digital traces, and impact the reliability of the information delivered via these traces. This study reveals that individuals can be classified into three behavioral profiles that differ in their degree of cooperation: collaborators, neutrals, and defectors. When there is no competition, digital traces spontaneously induce cooperation among individuals, highlighting the potential for stigmergic processes to foster collaboration in human groups. Likewise, competition between two groups also promotes cooperative behavior among group members who aim to outperform the members of the other group. However, intragroup competition can prompt deceptive behaviors, as individuals may manipulate their ratings to gain a competitive advantage over the other group members. In this situation, the presence of misinformation reinforces the use of private information over social information in the decision-making process. Finally, situations that combine both intragroup and intergroup competition display varying levels of cooperation between individuals, that we explain.

This research establishes the foundations for understanding stigmergic interactions in digital environments, shedding light on the relationships between competition, cooperation, deception, and decision-making. The insights gained may contribute to the development of sustainable and cooperative personalized decision-making algorithms and artificial collective intelligence systems grounded in stigmergy.

 

Matthieu VERDOUCQ – PhD defense

Defense in english

Team : Collective animal behaviour (CAB), CRCA-CBI

Supervisors : Guy THERAULAZ (CRCA-CBI) & Gautier HATTENBERGER (ENAC)

Committee members :

  • Pr. Sabine Hauert, Associate Professor, University of Bristol, Royaume-Uni (Rapporteure)
  • Dr. Franck Ruffier, Directeur de Recherches au CNRS, Aix-Marseille Université, France (Rapporteur)
  • Dr. Aurélie Dupont, Chargée de recherches au CNRS, Université Grenoble Alpes, France (Examinatrice)
  • Mme Marie-Pierre Gleizes, Professeure, Université Toulouse Paul Sabatier, France (Examinateur)
  • Pr. M. Gautier Hattenberger, Professeur, Ecole Nationale de l’Aviation Civile, Toulouse (Co-directeur de thèse)
  • Dr. Guy Theraulaz, CNRS, Directeur de Recherches au CNRS, Université Toulouse Paul Sabatier, France (Co-directeur de thèse)

 

Mathilde LACOMBRADE – PhD defense

Zoom link

Team : Navigation and Cognitive Ecology (BeeAntCE), CRCA-CBI

Supervisors : Mathieu LIHOREAU (CRCA-CBI) & Hervé Aubert (LAAS)

Committee members :

  • Claire Detrain, reporter
  • ​​​​​​Cédric Alaux, reporter
  • Jean Marc Devaud, examiner
  • Nathalie Volkoff, examiner
  • Antoine Couto, examiner
  • Mathieu Lihoreau, supervisor
  • Hervé Aubert, supervisor
  • Denis Thiéry, invited (and supervisor)
  • Fanny Vogelweith, invited (and supervisor)

© Photo credit : Romain Hacquet – @aker.romain

Emilie MAUDUIT – PhD defense

Defense in french

Zoom link

Team : Interindividual Variability and Emergent Plasticity (IVEP), CRCA-CBI

Supervisor : Raphaël Jeanson (CRCA-CBI)

Committee members :

  • Marlène Goubault-Body, Rapporteure (IRBI, Université de Tours)
  • Damien Charabidze, Rapporteur (CHJ, Université de Lille)
  • Audrey Dussutour, Examinatrice (CRCA, Université Toulouse 3)
  • Julien Bacqué-Cazenave, Examinateur (EthoS, Université de Caen)
  • Julien Cote, Examinateur (EDB, Université Toulouse 3)

Abstract :

Sociality, which represents a crucial step in the evolution of the complexity of living systems, has evolved repeatedly in vertebrates and invertebrates. Sociality covers an incredible variety of forms, from transitory groupings of usually solitary individuals to species living in integrated societies, called eusocial species. Although the transition to eusociality is still of great interest, this type of social organisation is not representative of the diversity of social forms in invertebrates. It is therefore necessary to identify the common features of all forms of social life in order to understand the origins of permanent sociality. The study of species with a transient social life is of particular interest, since in these species, juveniles live together for varying lengths of time, then disperse to live on their own. From a distal perspective, the ontogenic variations in social behaviour is probably accompanied by a change in the costs and benefits of group living. From a proximal point of view, the mechanisms that trigger the transition from a temporary and non-facultative social lifestyle to a solitary life are not yet understood. Spiders are a relevant model for understanding social transitions, as all spider species (> 51,500) exhibit a transient social phase: juveniles are gregarious and tolerants, then become solitary and aggressive as adults (except for 20 spider species that remain social throughout their lives). Previous work has shown that the social isolation that results from the natural dispersion of spiders triggers their aggression. The main objectives of my thesis were therefore to examine the communication modalities involved in maintaining social tolerance in the solitary spider Agelena labyrinthica, and to characterise the impact of social isolation on the perception and integration of social signals. By manipulating the social context during ontogeny in juveniles, we demonstrated the existence of an ontogenetic development of aggressiveness, revealed the existence of metabolomic differences according to the social context, showed that the onset of cannibalism does not result from a reduction in energy reserves, demonstrated that social tolerance can be restored after moulting, and finally observed that the maintenance of tolerance requires the perception of a signal emitted by a living spider. Through various behavioural approaches, this thesis suggests that the communication change underlying the decline of social tolerance in spiderlings involved a change in the perception and/or interpretation of communication signals by isolated individuals.

 

 

Weijia WANG – PhD defense

Defense in english

  Zoom link

Team : Collective Animal Behaviour (CAB), CRCA-CBI

Supervisor : Guy THERAULAZ (CRCA-CBI) & Zhangang HAN, Beijing Normal University

Committee members :

  • Pr. Wang Dahui, Beijing Normal University, Chine (Examinateur)
  • Pr. Zhixin Liu, Academy of Mathematics and Systems Science, Chine (Rapporteure)
  • Pr. Fernando Peruani, CY Cergy Paris Université, France (Rapporteur)
  • Pr. Nicolas Destainville, Université Toulouse Paul Sabatier, France (Examinateur)
  • Pr. Zhangang Han, Beijing Normal University, Chine (Co-directeur de thèse)
  • Dr. Guy Theraulaz, CNRS, Université Toulouse Paul Sabatier, France (Co-directeur de thèse)

Abstract:

Collective motion in groups of organisms is a ubiquitous phenomenon observed at all biological scales. From the collective migration of cells during a immune response to the collective response of fish schools to predators attacks, researchers have investigated the mechanisms that enables the coordination of movements and the formation of ordered structures in time and space in these living systems composed of a large number of constituents. It has been well established that the coordination of movements among individuals in a moving group results from a self-organization process, in which individuals repeatedly interact with their local neighbors. On the other hand, many existing computational models, due to their excessive simplification and lack of biological relevance, still face challenges in revealing the interaction rules from which collective motion emerges in various biological systems.. In this thesis, focusing on the challenging issues mentioned above, we have investigated the interacting rules involved in the emergence of collective states in data-driven fish school models. The models describe the interactions involved in burst-and-coast swimming in groups of Hemigrammus rhodostomus. We have first investigated the impact perceptual and cognitive factors on collective states. We then investigated the long-term collective behavior of schools in burst-and-coast swimming fish.

1. In natural conditions, social interactions can be modulated by the perceptual and cognitive abilities of animals as a result of adaptive fitness to the environment. The resulting collective states of the moving group will therefore change. To quantitatively investigate the impact of perceptual and cognitive factors on collective swimming mediated by social interactions, we comprehensively analyze the phase plane of a data-driven model that characterize social interactions involved in burst-and-coast swimming in schools of Hemigrammus rhodostomus. We find that coordinated swimming patterns of schooling and milling can emerge even if fish only interact with their most or two most influential neighbors, providing the existence of a minimal level of attraction between fish to maintain cohesion. We also find that the range of social interactions, which characterizes the perceptual ability of fish, has similar effects on collective states as the strength of interactions.

2. The burst-and-coast swimming mode is widely adopted by various species of fish. Fish are sensitive to the movements of other conspecifics in the burst phase, but neglect this information during the coasting phase. Therefore, this swimming mode potentially affects the coordination between fish. However, few studies have focused on the long-term collective behaviors of fish with a burst-and-coast swimming mode. We address this question by analyzing the phase plane and the long-term behavior with a model that quantitatively describes the general pattern of burst-and-coast swimming and social interactions between fish. We find that fish can effectively coordinate their behaviors in a broad range of interaction strengths when information about only one or two most influential neighbors is perceived. In long-term, the stability of schooling and milling states depends on whether group cohesion can be maintained.

Keywords : Collective Behavior, Self-organization, data-driven modeling, fish school.

Louis DEVERS – PhD defense

Defense in french

  Zoom link

Team : Collective Animal Behaviour (CAB), CRCA-CBI

Supervisor : Vincent Fourcassié (CRCA-CBI)

Committee members :

  • Audrey Dussutour, Directrice de recherche au CRCA-CBI (Toulouse)
  • François-Xavier Dechaume-Moncharmont, Professeur, Laboratoire d’Ecologie des Hydrosystèmes Naturels et Anthropisés, Université Claude Bernanrd Lyon 1
  • Thibaud Monnin, Directeur de Recherche, Institut d’Écologie et des Sciences de l’Environnement de Paris (iEES Paris), Sorbonne Université
  • Andrea Perna, Senior Lecturer, Assistant professor, IMT School for Advanced Studies in Lucca, Italy
  • Claire Detrain, Directrice de recherche au FRS – FNRS (Bruxelles)
  • Vincent Fourcassié, Directeur de recherche, CRCA-CBI (Toulouse)

Abstract :

Ants are well known for their capacity to self-organize and for their feats in foraging and transport activities, that they are able to achieve with relatively limited cognitive capacities. They are able to solve with disconcerting ease complex problems, such as finding the shortest paths among several options, ensuring the thermoregulation of a nest or regulating the colony’s energy and nutrients intake. The solution to a collective problem in ants emerges from the sum of simple, local interactions between them and their environment (by depositing pheromones, for instance). Ants are therefore a relevant model for studying decision-making processes at the interface between simple, cognitively limited individuals and a complex, relevant or even optimal collective.

One of the tasks in which ants excel is transport. In fact, they are one of the few group of species that can move objects of significant mass over long distances. In particular, they are able to organise themselves around a load and to carry it collectively in a way that allow them to overcome their individual limitations. Load-carrying tasks are omnipresent during foraging, nest building and brood care, and are therefore essential for the colony. Each decision to carry an object from point A to point B entails a potentially significant energy cost for the ants. Therefore, a form of effort regulation can be expected. The aim of this thesis is to study decision-making processes in ants in the context of load transport in relation with the energy costs produced. The main question motivating our research is therefore: what role does energy regulation play in the decision-making processes underlying load transport in ants?

This thesis consists of two chapters dealing with the same question studied on two different species in two different contexts. Firstly, we studied load transport in a binary choice task taking place during the clearing of an underground gallery in the species Messor barbarus. Secondly, we examined the impact of load mobility in a context of collective transport in the species Aphaenogaster senilis.

We quantified the quality of the transports performed by ants using objective measures, such as efficiency and mechanical work with mechanical models designed for this thesis. We focused on mandibular grasps on the load as the basis of load transport behaviour. Mandibular grasps mark indeed both the initiative of the transport (at the start of the grasp) and the persistence on the task (through their duration).

We observed that ants, when faced with a choice between two options to remove an object blocking a gallery with different inclinations, pulled the load towards the side requiring the least mechanical work in 75% of cases. However, while individual ants seem to solve this task efficiently, the efficiency remains relatively low at the collective level. We also observed that while the duration of mandibular grasps was shorter on tough tasks, the amount of energy expended remained unchanged. The amount of energy expended seems to depend on the muscular capacities of the ants, which suggests that they make a similar relative effort at each transport attempt.

During collective transports, we observed that ants did not arrange themselves randomly around the transported load. The arrangements preferred by ants are those that reduce the total forces required to keep the object above ground. This preference disappears when the load is held still by a pin. We also noted that disadvantageous arrangements are abandoned more quickly than others, showing a form of energetic regulation of behaviour on the task.

 Keywords : Quantitative ethology, Decision making, Load transportation, Optimisation, Collective behavior, Ants

Manon TERNOIS – PhD defense

PhD defense in french

Zoom link

Teams : IVEP (CRCA-CBI) & NNCED (CIRIMAT)

Supervisors : Audrey Dussutour (CRCA-CBI) & Emmanuel Flahaut (CIRIMAT)

Committee members :

  • Mme Anna Bencsik, ANSES site de lyon, Rapporteure
  • Mme Catherine Santaella, CNRS Institut de Biosciences et Biotechnologies d’Aix-Marseille Université, Rapporteure
  • Mme Mélanie Auffan, CNRS CEREGE, Examinatrice
  • Mme Noélie Davezac, CNRS CRCA-CBI, Examinatrice
  • Mme Audrey Dussutour, CNRS CRCA-CBI, Directrice de thèse
  • Emmanuel Flahaut, CNRS CIRIMAT, Co-directeur de thèse

Abstract :

Carbon nanotubes (CNTs) are carbon nanomaterials with industrial development having reached a stage of maturity enabling them to be used in many everyday applications (composite materials, coatings, energy storage, biomedical, etc.). They are a source of concern for human and environmental health because they can be released into the environment at each stage of their life cycle (production, use and end-of-life of finished products). Even though studies relating to their potential impact on health and the environment started some fifteen years ago, many questions remain unanswered.

The aim of this thesis is to assess the effects of CNTs (we used double-walled CNTs (DWCNTs) as representatives of all the different types of CNTs) on an emerging cellular model at the interface between environmental toxicology and cellular toxicology: the myxomycete Physarum polycephalum. On the one hand, P. polycephalum lives mainly in soil litter, a medium that receives and concentrates pollution, where it plays an essential role in the ecosystem by actively participating in the recycling of organic matter. In addition, the simple organization of P. polycephalum (a unicellular eukaryote) enabled us to assess the internalization and bioaccumulation of CNTs within the cell. Finally, the behavioral complexity of P. polycephalum (problem solving and adaptation of their behavior to environmental diversity) enabled us to measure the effects of CNTs on different behavioral variables such as migration speed and decision making. We first demonstrated that CNTs are internalized in the cell, do not bioaccumulate and are rapidly excreted. We then demonstrated that CNTs induce variable effects on the behavior of P. polycephalum (slowed or accelerated speed, optimal or non-optimal decision-making), which differ depending on the strain used, the duration of exposure, the exposure concentration and the substrate used. By combining exposure to CNT with other stress factors (aversive compound, ageing, temperature), we observed a behavioral response that remains extremely variable.

This work shows that CNTs have moderate and difficult-to-quantify effects on the behavioral response of P. polycephalum. In the future, it will be interesting to examine the effects of CNTs on the physiological and molecular response of this organism.

© Photo : Romain Hacquet – @aker.romain

 

Léo CLEMENT – PhD Defense

PhD defense in english

 Zoom link : https://us06web.zoom.us/j/86474991977

Team : BeeAntCE

Supervisors : Antoine WYSTRACH & Jacques GAUTRAIS

Committee members :

  • M. Andrew PHILIPPIDES, University of Sussex, Rapporteur
  • Mme Emily BAIRD, Stockholm University, Examinatrice
  • M. Antoine WYSTRACH, CNRS, Co-directeur de thèse
  • M. Franck RUFFIER, CNRS – Institut des Sciences du Mouvement Marseille, Examinateur
  • Mme AUDREY DUSSUTOUR, CNRS, Examinatrice
  • M. Simon BENHAMOU, CNRS / CEFE, Rapporteur

Abstract :

Navigation in natural environments is an essential ability for animals, but it can be highly challenging to achieve due to the complex, ever-changing, nature of the environment they navigate through. Solitary foraging hymenopterans, such as ants, have evolved remarkable abilities to navigate in these complex environments despite a nervous system much simpler than those of vertebrates. What’s more, ants’ displacements can be easily tracked, thus providing a powerful system to investigate the mechanisms underlying navigation in the wild.

Thanks to the development and application of neurobiological tools in insects, we now have an increasingly detailed description of the circuits in these “mini-brains”. These networks, composed of a large number of interacting units (neurons), are the site of very dynamic internal activity that allows for an effective coupling of the organism with its environment. The field of insect navigation has integrated this neurobiological knowledge with a long-standing tradition of behavioural experiments, as well as in-silico modelling approaches, to gain a deeper understanding of the mechanisms and emergent properties in these systems. This multi-level approach has provided valuable insights into how complex behaviour emerges.

This thesis presents an integrative approach combining behavioural experiments and computational modelling with the aim to gain further understanding of the mechanisms of ant navigation.

First, I investigate the dynamics of visual learning when ants navigate in natural conditions. There are already good insights into how the insect brain can memorize and recognize views, and how these views might be used for navigation. However, practically nothing is known about how learning is orchestrated in the first place. Learning a route cannot be governed only by rewards and punishments but may happen ‘continuously’; a vague concept so-called ‘latent learning’ in the vertebrate literature. By combining field experiments and modelling, I show that ants learn the route they travel in a continuous fashion. I also explain how such a continuous mechanism of learning and recalling can be implemented in the light of the known insect brain circuitry. Our work shows that such a continuous spatial learning is supported by egocentric route memories rather than a map-like reconstruction of space.

Secondly, I shed light on how higher-level visual recognition and lower-level motor control interact. Most -if not all-studies in animal navigation have focused on higher level strategies such as the use of path integration, the recognition of learnt visual cues and the reconstruction of so-called cognitive maps. However, how these higher-level strategies are supported by lower level (often more ancestral) motor behaviours remains largely unexplored. We used a multidirectional treadmill set up -a trackball- to record with high precision the motor behaviour of ants directly in their natural environment. Results explain how higher-level navigation strategies are supported by lower-level motor control and demonstrate the existence – and importance – of an intrinsic oscillator at the core of navigational behaviours.

Finally, I investigate the specific cues encoded by ants in visual scenes. Insects’ visual system performs various feature extractions. I used virtual reality (VR) to explore which visual cues are encoded by ants to consider the presence of a natural panorama and trigger exploratory behaviours. Through this approach, I shed light on the perceptual encoding of naturalistic environments and provide a promising avenue for further investigation using virtual reality setups.

Taken together, this thesis allowed me to understand that behaviour, rather than being a set of discrete actions, is a continuous process where intelligence can be seen as an emergent property. I employed various approaches, some successful, some failing, but all improved my vision of how I should ask and answer a scientific question.