Catégorie d'événements: 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

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.

PhD defense in english

  https://univ-tlse3-fr.zoom.us/j/98820467021?pwd=RzRGb0NmNVVPZUVKeHdibjh6ZFhGQT09

Team : PRADA (EDB)

Supervisors : Guillaume Isabel (CRCA-CBI) et Jean-Louis Hemptinne (EDB)

Committee members :

• Examinateur: Director of Research Etienne Danchin, Université Toulouse III
• Co-directeur: Prof. Guillaume Isabel, Université Toulouse III
• Examinateur: Prof. Paul Seabright, Université Toulouse I
• Examinateur: Dr. Sabine Noebel, Martin-Luther-University
• Rapporteur: Prof. Andrew Whiten, University of Saint Andrews
• Rapporteur:  Prof. Boris van Leeuwen, University of Tilburg
• Rapporteur: Prof. Jean-Christophe Billeter, University of Groningen

Abstract :

Social learning encompasses all the distinct ways an individual learns from others and has already been identified in many non-human vertebrate and invertebrate species. Conformity, the disproportionate copying of the most common trait in a group, has come to the fore as a major driver in the emergence of culture.

In this interdisciplinary thesis, I study social learning, conformity and related processes in both humans (Homo sapiens, Chapter I) and the fruit fly (Drosophila melanogaster, Chapter II), to (1) build a better understanding of these phenomena across species; (2) find commonalities and differences between these two species; (3) help elucidate the nature of human conformity and (4) contribute to reconciling the distinct approaches from different disciplines.

In the first chapter, we used a novel experimental tool-set in two online experiments in humans to test the role of social information in people’s perception of their environment This provides evidence for conformity in two different contexts. Finally, we tested whether conformity is stronger in mate choice (as suggested by our colleagues in Toulouse), but find no evidence for it when compared to the alternative decision domain of ratio estimation.

In the second chapter, we focused on mate-copying in D. melanogaster to investigate how individuals adjust their behavior in response to social information that changes over time, specifically how they deal with sequentially presented items of conflicting social information. To tackle this question, we used a new video recording protocol in an experiment with two demonstrations one after the other, each consisting of an image of a model female copulating with a different male phenotype. Unexpectedly, in our experimental design, females tended to prefer the male phenotype of the first demonstration, which is suggestive of a primacy bias, defying the intuition that social learning would prioritize recent social information that should, in theory, reflect more accurately the current environment.

PhD defense in french

Zoom link : https://univ-tlse3-fr.zoom.us/j/99182743985

Team : REMEMBER

Supervisor : Lauve VERRET (CRCA-CBI)

Committee members :

• Bertrand Lamboblez – rapporteur
• Hélène Marie – rapporteure
• Francesca Sargolini – rapporteure
• Vincent Fourcassié – examinateur
• Laure Verret – directrice de thèse

Abstract :

Alzheimer’s disease (AD) is associated with abnormal brain activity that underlies cognitive deficits. It is now well-established that dysfunction of GABAergic neurons expressing parvalbumin (PV) protein contributes to these alterations in brain activity—and thus to cognitive impairment—in mouse models and AD patients. In the adult brain, PV neurons are frequently associated with a specialized form of extracellular matrix, the perineural net (PNN), the presence of which would contribute to the long-term maintenance of a PV-dependent brain network. We recently demonstrated that the presence of PNN around PV cells is reduced in the hippocampus of the Tg2576 mouse model of AD, and that it could contribute to the memory deficits observed in this model. Furthermore, young adult Tg2576 mice exposed to an enriched environment (EE) show an increase in the number of quantifiable PV/PNN interneurons in the hippocampus, as well as long-lasting cognitive improvement.

In this thesis, we tested the hypothesis that environmental stimulus-induced remodeling of hippocampal PV/PNN interneurons is required for cognitive improvement of Tg2576 mice. To address this question, in a first study we sought to prevent EE-dependent remodeling of PV interneurons and their PNN in hippocampal area CA1 specifically—via a targeted injection of chondroitinase-ABC (ChABC)—and observed that this is sufficient to suppress the beneficial effects of EE on spatial memory performance (CA1-dependent), without affecting social memory improvements (CA2-dependent). This strongly suggests that the beneficial effects of EE on memory performance in AD mouse model is underpinned, at least partially, by an increase in the activity of hippocampal PV neurons and/or the presence of PNN. Furthermore, based on recent studies, we investigated whether exposing Tg2576 mice to visual and/or auditory stimuli at gamma frequency (40Hz) mimics the effects of a stay in EE on PV/PNN remodeling and memory performance. This experiment did not provide conclusive results on the potential effects of multimodal gamma stimulations on PV interneurons. Finally, we used the innovative high-resolution microscopy technique Random Illumination Microscopy (RIM) to determine whether the differences in PNN numbers observed under different experimental conditions (Tg2576 and non-transgenic mice, exposed or not to EE, injected or not by ChABC) are accompanied by remodeling of the presence of perisomatic synapses on hippocampal PV neurons.

Thus, our work identifies PV neurons and their extracellular matrix PNN as key players in the long-term behavioral improvement of AD mice following early environmental stimuli, making them therapeutic targets of interest for fighting cognitive disorders associated with the pathology.

Presentation in english

Supervisors : Isabelle Massou and Martin Giurfa

Comitee members :

• M. Claudio LAZZARI (Université de Tours) – Reviewer
• Mme Emmanuelle JACQUIN-JOLY (INRAE iEES – Paris) – Reviewer
• M. Cédric ALAUX (INRAE Avignon) – Examiner
• Mme Isabelle MASSOU (Research Centre of Animal Cognition) – Thesis co-supervisor
• M. Martin GIURFA (Research Centre of Animal Cognition) – Thesis co-supervisor

Abstract :

Honey bees are endowed with the capacity of color vision as they possess three types of photoreceptors in their retina that are maximally sensitive in the ultraviolet, blue and green domains owing to the presence of corresponding opsin types. While the behavioral aspects of color vision have been intensively explored based on the easiness by which free-flying bee foragers are trained to color stimuli paired with sucrose solution, the molecular underpinnings of this capacity have been barely explored. Here, to fill this void, we explore opsin properties and gene expression changes in the bee brain, during color learning and retention in controlled laboratory protocols.

We characterized opsin distribution in the honey bee visual system, focusing on the presence of two types of green opsins (Amlop1 and Amlop2), one of which (Amlop2) was discovered upon sequencing of the bee genome. We confirmed that Amlop1 is present in ommatidia of the compound eye but not in the ocelli, while Amlop2 is confined to the ocelli. We developed a CRISPR/Cas9 approach to determine possible functional differences between these opsins. We successfully created Amlop1 and Amlop2 adult mutant bees by means of the CRISPR/Cas9 technology and we also produced white-gene mutants as a control for the efficiency of our method. We tested our mutants using a conditioning protocol in which bees learn to inhibit attraction to chromatic light based on electric-shock punishment (Icarus protocol). White and Amlop2 mutants learned to inhibit spontaneous attraction to blue light while Amlop1 mutants failed to do so. These results indicate that responses to blue light, which is also partially sensed by green receptors, are mediated mainly by compound-eye photoreceptors containing Amlop1 but not by the ocellar system in which photoreceptors contain Amlop2. Accordingly, 24 hours later, white and Amlop2 mutants exhibited an aversive memory for the punished color that was comparable to control bees but Amlop1 mutants exhibited no such memory. We discuss these findings based on controls with eyes or ocelli covered by black paint and interpret our results in the context of chromatic vs. achromatic vision via the compound eyes and the ocelli, respectively.

Finally, we analyzed immediate early gene (IEG) expression in specific areas of the bee brain following color vision learning in a virtual reality (VR) environment. We changed the degrees of freedom of this environment and subjected bees to a 2D VR, in which only lateral movements of the stimuli were possible and to a 3D VR which provided a more immersive perception. We analyzed levels of relative expression of three IEGs (kakusei, Hr38, and Egr1) in the calyces of the mushroom bodies, the optic lobes and the rest of the brain after color discrimination learning. In the 3D VR, successful learners exhibited Egr1 upregulation only in the calyces of the mushroom bodies, thus uncovering a privileged involvement of these brain regions in associative color learning. Yet, in the 2D VR, Egr1 was downregulated in the OLs while Hr38 and kakusei were coincidently downregulated in the calyces of the MBs in the group that learned. Although both VR scenarios point towards specific activations of the calyces of the mushroom bodies (and of the visual circuits in the 2D VR), the difference in the type of expression detected suggests that the different constraints of the two VRs may lead to different kinds of neural phenomena. While 3D VR scenarios allowing for navigation and exploratory learning may lead to IEG upregulation, 2D VR scenarios in which movements are constrained may induce higher levels of inhibitory activity in the bee brain. Overall, we provide a series of new explorations of the visual system, including new functional analyses and the development of novel methods to study opsin function, which advances our understanding of honey bee vision and visual learning.

Keywords: Vision, Visual Learning, Honey Bee (Apis mellifera), Opsin Genes, Photoreceptors, CRISPR/Cas9, Inhibition of Color Attraction, Virtual Reality, Brain, IEG expression, Mushroom Bodies, Optic Lobes.