Catégorie d'événements: PhD defense

Defense in french

Zoom link : https://cnrs.zoom.us/j/91517327506?pwd=222uKN9CfbNWporpa4RkpSIS1YtGJQ.1

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

Supervisors : Pierre Moretto (CRCA-CBI) and Vincent Fourcassié (CRCA-CBI)

Committee members :

• Anthony Herrel, Rapporteur
• Claudio Lazzari, Rapporteur
• Annick Abourrachid, Examinatrice
• Audrey Dussutour, Examinatrice
• Julien Serres, Examinateur
• Vincent Fourcassié, Directeur de recherche
• Pierre Moretto, Directeur de recherche

Abstract :

Division of labour in social insects has long been a topic of interest in ethology. Among social insects, some species are characterized by a polymorphism of the worker caste, where the role of individuals in the colony is often directly linked to their external morphology. In some of these species, for example, the largest individuals, generally called soldiers, defend the colony. However, it is sometimes more difficult to establish this link for certain tasks, such as load-carrying in ants. A case in point is he granivorous ant Messor barbarus that we studied in this thesis. This species shows a division of labour in load carrying among workers of its different morphs called minor, media and major, that cannot be explained simply by differences in their external morphology. Our hypothesis is that this division of labour could be explained by differences in the characteristics of the muscular system of the individuals, as well as by the organization and biomechanical properties of their exoskeleton.

In order to test this hypothesis, we have used in this work a biomechanical approach to study load-carrying behaviour in ants, which integrates functional morphology and even goes so far as to create numerical models inspired by biorobotics. Biomechanics has always been applied to understanding the mechanisms that generate movement and their efficiency. It can now also offer realistic simulations that can be used, for example, to generate locomotor patterns that optimize a constraint. Comparison with experimentation can then provide answers to certain hypotheses about the emergence of an individual, or even collective, locomotor pattern. This approach is known as reverse engineering. Developed here specifically at the scale of the ant, this approach has enabled us to study the coordination of the different segments of a single individual (part IV), or even several segments in the case of collective transport (part VI), and to address the question of the coordination of the muscles that control the head of an ant when it carries a load in its mandibles (part V).

To achieve these results, which are still preliminary, we developed a realistic digital model of the ant muscular system using the Opensim software, which involved integrating structural data identified through X-ray microtomography (part III) and 3D kinematic data reconstructed from videos acquired by synchronized high-resolution cameras (part IV). Our digital avatar has yet to be completed, but it has already been used to optimize our 3D kinematic data, to discuss the roles assigned to the different muscles of the thorax and to address the dynamic coordination of the different muscles involved in joint control. Ultimately, this model could be developed and adapted for application to workers of different morphologies, such as those found in the species Messor barbarus. It may then be used to explain the origin of the different load-carrying performances observed between individuals of different morphs in this species. It could also provide a link between the different approaches used to understand the origin and underlying mechanisms of ant behavior, i.e., phylogeny, ecology, biology, ethology, biomechanics and biomimetics.

Defense in french

Zoom link : https://cnrs.zoom.us/j/93347143064?pwd=00GKwwWtuJED8vkIiaM2N66RMUahRN.1

Team : EXPLAIN (Experience-Dependent Plasticity in Insects) – CRCA-CBI

Supervisors : Séverine TRANNOY (CRCA-CBI) et Audrey DUSSUTOUR (CRCA-CBI)

Committee members :

• Mme Maria-Cristina LORENZI, Rapporteure, Université Sorbonne Paris Nord, LEEC
• Serge BIRMAN, Rapporteur, CNRS, ESPCI
• Mme Tihana JOVANIC, Examinatrice, CNRS, NeuroPSI
• Jean-Marc DEVAUD, Examinateur, Université Toulouse III – Paul Sabatier, CBI-CRCA
• Mme Audrey DUSSUTOUR, Directrice de thèse, Université Toulouse III – Paul Sabatier, CBI-CRCA
• Mme Séverine TRANNOY, Co-directrice de thèse, CNRS, CBI-CRCA

Abstract :

Social aggressive and reproductive behaviours are vital for most animals. In one hand, they assure the access to primary resources such as food or mates. On the other hand, they assure offspring and species sustainability. Our aim was to understand how aggressive interactions and their result (victory or defeat) impact males’ reproductive behaviours. Then, we studied the fundamental mechanisms underlying aggressive behaviours dysregulation. For such purposes, we used Drosophila melanogaster as a model. We showed that losers lack of motivation one hour after the defeat in non-competitive context. In competition, losers showed impaired courtship behaviours which are not the consequence of a misperception from the male nor a preference from the females. We then identified two neurons involved in the dysregulation of aggression: the VPM4 and the MBON-11. VPM4 are double-neurotransmissing neurons: they use both glutamate and octopamine as neurotransmitters. We showed that glutamate allowed the regulation of aggression. It inhibits MBON-11 through GluClα receptors. dTrpA1-induced activity in MBON-11 provoked boxing events to occur, and we demonstrated that GABA transmission from MBON-11 is responsible. This thesis is the first step in the comprehension of the emergence of hyper aggressive events in drosophila, and ask the question of the consequence of such dysregulation for individuals’ behaviours.

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.

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.

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

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.