Thèse Influence du Sexe sur les Comportements Sociaux chez les Juvéniles d'Araignées Solitaires H/F - Doctorat.Gouv.Fr

Établissement : Université de Toulouse École doctorale : SEVAB - Sciences Ecologiques, Vétérinaires, Agronomiques et Bioingenieries Laboratoire de recherche : CRCA - Centre de Recherches sur la Cognition Animale Direction de la thèse : Raphaël JEANSON ORCID 0000000268118123 Début de la thèse : 2026-10-01 Date limite de candidature : 2026-06-01T23:59:59 La socialité représente une transition évolutive majeure. Le maintien de la cohésion sociale chez les juvéniles est considéré comme la voie principale pour l'émergence d'une vie sociale permanente. Les araignées sont des modèles pertinents pour initier des études comparatives et explorer les mécanismes impliqués dans ces transitions. Bien que la majorité des 54 000 espèces sont solitaires à l'âge adulte, toutes présentent une phase grégaire transitoire aux stades précoces du développement et 20 espèces d'araignées sociales ont été décrites. Nos travaux antérieurs ont montré que la perte de tolérance sociale chez les araignées solitaires résulte de l'isolement consécutif à la dispersion : les juvéniles élevés en groupe restent tolérants, tandis que ceux élevés seuls deviennent agressifs. Cependant, l'influence du sexe sur l'expression de ces comportements sociaux chez les juvéniles n'a jamais été étudiée. Ce projet propose donc d'explorer cette question en combinant des approches éthologiques et de biologie moléculaire afin de déterminer si le sexe module l'expression de la plasticité comportementale des juvéniles et leur capacité à maintenir une cohésion sociale. Our research focuses on the social behaviours in spiders. Among the 54,000 species of spiders, about 20 species have developed a sophisticated social life characterised by the building of a common web, cooperation in brood care and hunting[1,2]. The most sophisticated forms of cooperation have evolved under tropical latitudes, which offer favourable ecological conditions (e.g. year-round food supplies, absence of marked seasons). Interestingly, all social species are nested within solitary species genera, and evidence support as many as eighteen independent origins of sociality, with species broadly distributed across taxonomically distinct families[3]. One privileged route to permanent sociality in arthropods involves the loss of premating dispersal and implies the extension of the phase of social cohesion among juveniles (e.g. subsocial route)[4].

While a solitary lifestyle characterises the vast majority of species at adulthood, all spider species undergo a transient gregarious phase during the early developmental stages before dispersal. The duration of the gregarious phase in spiderlings is a plastic trait, which depends on the interplay between maturational processes and the response to environmental fluctuations, notably in food availability. In solitary spiders, pre-dispersing juveniles, irrespective of their nutritional state, are highly reluctant to attack and cannibalise conspecifics[5]. This markedly contrasts with the behavioural patterns observed at later developmental stages where the expression of tolerance depends on environmental conditions, notably on food availability[5-7]. In social spiders, however, tolerance persists throughout life and seems independent of environmental constraints (although group-level properties such as colony size in social spiders can vary across habitats[8]). Understanding social transitions in spiders therefore requires to identify the proximal mechanisms driving the decline of social cohesion and the onset of dispersal in juveniles.

In our earlier work in the solitary species Agelena labyrinthica [9-15], we demonstrated that (i) social cohesion in pre-dispersal spiderlings involves mutual attraction, (ii) pre-dispersal spiderlings are highly reluctant to cannibalise same instar conspecifics, (iii) there is no evidence of kin discrimination in pre-dispersal spiderlings, (iv) the first moult out of the cocoon coincides with important changes in cuticular profiles and the onset of aggressive interactions, (v) fasting influences aggressiveness in post-dispersing juveniles, (vi) aggressiveness results from social isolation, (vii) moulting can restore social tolerance in aggressive spiderlings and (viii) the expression of tolerance requires the production of a presumed life signal. To date, however, no study has examined whether sex can influence the behaviour of juveniles in any species of spiders. This is because sexual morphological characteristics appear relatively late in development, after several moults. To determine the sex of spiderlings, markers on the sex chromosomes must be used. We have recently sequenced the genome of our model spider and developed such sex markers. We can now conduct behavioural studies to determine whether social behaviours differ between males and females in the very early stages of development, and to examine how this correlates with changes in physiological pathways.

This project builds on our previous findings and focuses on the following objectives:
- We will determine the sex of spiderlings using molecular biology approaches for which we have developed in-house expertise in order to compose groups of different sizes with known sex ratios (pure male or female groups) to examine whether sex influences the expression of tolerance at different developmental stages and the onset of dispersal.
- We will use metabolomic approaches as part of an already effective collaboration to identify physiological changes that may accompany sexual differences in social behaviour. The main objective is to study the influence of sex on the expression of social behaviours in solitary spiderlings. This project integrates behavioural, molecular, and metabolomic approaches to investigate the role of sex in shaping social behaviours in juvenile spiders.
- Molecular biology approach: Spiderlings will be sexed using a non-lethal method that leverages the natural autotomy ability of spiders, allowing for DNA extraction followed by qPCR analysis.
- Behavioural approach: Juvenile spiders of known sex will be reared either individually or in groups and assessed at later developmental stages-following our established protocols-to determine whether sex influences social behaviours, such as mutual attraction, dispersal or aggressiveness.
- Metabolomic approach: Metabolomic techniques will be employed to identify physiological changes associated with potential sex-based differences in social behaviour.

La candidate ou le candidat devra avoir une solide formation en sciences du comportement, idéalement associée à des compétences en biologie moléculaire.