Raphaël Jeanson

Long-term dynamics in proximity networks in ants

Social insects rely extensively on interactions to coordinate their activities. Some studies have recently explored several attributes of insect colonies from a network perspective, providing evidence of variation in connectivity patterns among group members. The temporal stability of interaction networks, however, has rarely been examined. In this study, ants of the species Odontomachus hastatus were individually equipped with passive microtransponders to collect their spatial positions in artificial nests automatically. Colonies were surveyed for 3 consecutive weeks to build weighted networks of proximity between ants. The analysis revealed important interindividual differences in connectivity patterns and showed that proximity networks were stable over time. The removal of the queen did not impact the patterns of association between workers, confirming that she did not contribute to shaping network structure. Ants forming long-lasting associations with a small number of nestmates exhibited a reduced tendency to move. In contrast, mobile workers were more likely to interact homogeneously with their nestmates and did not display any privileged associations.

Genetic variation in aggregation behaviour and interacting phenotypes in Drosophila

Aggregation behaviour is the tendency for animals to group together, which may have important consequences on individual fitness. We used a combination of experimental and simulation approaches to study how genetic variation and social environment interact to influence aggregation dynamics in Drosophila. To do this, we used two different natural lines of Drosophila that arise from a polymorphism in the foraging gene (rovers and sitters). We placed groups of flies in a heated arena. Flies could freely move towards one of two small, cooler refuge areas. In groups of the same strain, sitters had a greater tendency to aggregate. The observed behavioural variation was based on only two parameters: the probability of entering a refuge and the likelihood of choosing a refuge based on the number of individuals present. We then directly addressed how different strains interact by mixing rovers and sitters within a group. Aggregation behaviour of each line was strongly affected by the presence of the other strain, without changing the decision rules used by each. Individuals obeying local rules shaped complex group dynamics via a constant feedback loop between the individual and the group. This study could help to identify the circumstances under which particular group compositions may improve individual fitness through underlying aggregation mechanisms under specific environmental conditions.

Responses to nutritional challenges in ant colonies

In social insects, food collection for the entire colony relies on a minority of its workers. How can the colony choose between resources, determine the task allocation of workers and exhibit a flexible food storage strategy from the foraging decisions taken only by a minority? We addressed this question by posing nutritional challenges to trap-jaw ants, Odontomachus hastatus, and explored their response in terms of survival, foraging behaviour and energy storage. In the first challenge, ants alternated between long periods of confinement to a high-protein diet and short periods of confinement to a high-carbohydrate diet. In the second challenge, ants alternated between long periods of confinement to a high-carbohydrate diet and short periods of confinement to a high-protein diet. In the third challenge, ants were given simultaneously a high protein and high-carbohydrate diet. First, we showed that (1) mortality increased with protein consumption, (2) a brief exposure to a high-carbohydrate diet lessened the negative consequence of high protein consumption and (3) ants given a choice of complementary diets regulated intake and minimized mortality. We also demonstrated that ants used an energy-saving strategy to overcome challenging nutritional environments. In addition we showed that the ants had an extraordinary capacity to regulate the amounts of food entering the nest both at the collective level by allocating more workers to foraging on a high-protein diet and at the individual level by collecting more food on a high-carbohydrate diet. Our study provides new insights into the strategies used by ants facing nutritional challenges and deepens our understanding of the nutritional ecology of ants and, thereby, their vast ecological success.

Ontogenesis and dynamics of aggregation in a solitary spider

Agelenidae interattraction ontogenesis simulation spider Aggregation is a prerequisite for transitions from a solitary to a social life. One evolutionary route to sociality implies the maintenance of cohesion among juveniles. The study of the influence of ontogenesis on mutual tolerance appears of fundamental importance for understanding social transitions. Spiders are particularly relevant models to address these questions. All solitary spiders have a transient gregarious phase prior to their dispersal and solitary and social species are included within the same genus. We characterized the patterns of aggregation during ontogenesis in the solitary spider Agelena labyrinthica. Our results showed that the intensity of aggregation in solitary spiderlings declined from the day of emergence to the sixth week. We developed an agent-based model implementing behavioural rules measured experimentally to explore their relative contribution in the ontogenetic shift in social behaviours observed in solitary spiders. Combining experimental and theoretical approaches, we demonstrated that aggregation relied on a modulation of individual behaviours depending on the number of conspecifics perceived locally and that the decline in aggregation with age relied on variations in the strength of interattraction occurring during ontogenesis.

Early experience and social performance in spiderlings

The social context experienced during early ontogeny can have lifelong consequences on the expression of social skills, and social isolation during development frequently impairs social competence. In this study, we used spiders as a model to investigate whether early social experience shapes social performance later in life. In spiders, the juveniles of all species show a transient gregarious phase that extends after their emergence from the maternal cocoon and ends with the initiation of agonistic interactions and cannibalism. Most studies that investigated social interactions in spiderlings focused on kin recognition. However, the potential mechanisms shaping recognition and discrimination, and particularly the role of early social experience, received little attention. Therefore, we examined to what extent early social isolation can influence the expression of social behaviours. We also investigated the influence of familiarity and kinship, and of their interaction with social experience on the expression of cannibalism. Our results showed that social isolation of spiderlings of Agelena labyrinthica since the egg stage did not influence social performance after emergence. Our study advocates for the existence of a species-specific chemical signature inhibiting cannibalistic tendencies in spiderlings.

Caste discrimination in the ant Odontomachus hastatus: What role for behavioral and chemical cues?

In social insects, the maintenance of genetic colony integrity requires resident workers to recognize any intruder with a reproductive potential and to behave appropriately to minimize fitness costs. In this study, our objective was to identify the relative contribution of the behavioral patterns and chemical cues of intruders with different fertility status on their likelihood of being accepted in monogynous colonies. Using the ponerine ant Odontomachus hastatus as a model organism, we introduced non-nestmate workers, founding queens and heterospecific workers on intact nests in the field. We demonstrated that resident workers were more aggressive toward founding queens than toward non-nestmates workers originating from the same or a distant population. Lab experiments showed that the patterns of aggression did not differ substantially between chilled and live ants, which suggests that chemical cues alone allow caste discrimination. However, the absence of behavioral cues produced more variable results in the outcome of interactions. We also showed that resident workers readily accepted non-nestmate mature queens. The analysis of cuticular profiles revealed that individuals belonging to different castes and fertility status have contrasted chemical signatures. Overall, our study revealed that workers exhibit a graded behavioral response depending on the reproductive status of intruders. We discussed the observed variation in the extent of aggression in relation to the potential fitness costs associated with acceptance or rejection error of individuals differing in fertility status.

Analysing plant–pollinator interactions with spatial movement networks

1. Pollinators, such as bees, face the complex challenge of efficiently exploiting patchily distributed floral resources across large landscapes.

Cannibalism in spiderlings is not only about starvation

Many species show a transient group life, and dispersal often coincides with the onset of agonistic behaviors. Changes in the nature of interactions among conspecifics can rely on a variation in the production of communication cues and/or on a switch in the processing of social information. The relative contribution of each process on the initiation of aggression still remains to be investigated. Spiders constitute relevant models to address this issue since all solitary species undergo a transient gregarious phase prior dispersal. In this study, we developed a combination of behavioral and physiological assays to examine the mechanisms accompanying the onset of agonistic interactions in spiderlings of the solitary species Agelena labyrinthica. Juveniles of different developmental stages were supplied with diets differing in prey availability. We showed that unfed spiderlings never molted, retained their cuticular lipid signature, and did not behave aggressively. This contrasted with fed individuals that molted, changed their cuticular profiles, and displayed agonistic interactions and cannibalism. We demonstrated that depletion in lipid stores was not sufficient to elicit aggression or cannibalism. Our analysis also revealed that major shifts in cuticular profiles only occurred after the first molt outside the cocoon. The lack of agonistic interactions in unfed spiderlings suggests an absence of behavioral plasticity in response to food shortage at the earliest developmental stages. We propose that the initiation of aggression relies more on a shift in the production of cuticular cues accompanying molting rather than on changes in information processing depending on the physiological state of individuals.Significance statementMost species of spiders display a transient gregarious phase preceding the initiation of agonistic interactions and dispersal. We examined what factors are associated with the onset of aggression in gregarious juveniles and we showed that pre-dispersing spiderlings despite low energetic stores never cannibalized conspecifics. This contrasts with later instars that displayed increased levels of aggression. The initiation of agonistic interactions coincided with major changes in the profiles of cuticular lipids, which are used in spiders to regulate social interactions. Our study suggests that depletion of lipid stores is not sufficient to trigger aggression but that it likely requires changes in communication cues associated with molting. We propose that the absence of behavioral plasticity of pre-dispersing juveniles in response to starvation allows spiderlings to maintain social cohesion and to benefit from the potential advantages granted by gregariousness, irrespective of environmental fluctuations.

Division of labor as a bipartite network

We present metrics developed in community ecology that are relevant to quantify division of labor, which is a recurrent feature of insect societies. Under a network perspective, workers are connected to the tasks they are engaged in and tasks are linked to the workers that perform them. Because workers and tasks belong to different classes, division of labor can be modeled as a bipartite network.

Onset of fights and mutual assessment in ant founding queens

ABSTRACT In animals, the progress and outcome of contests can be influenced by an individuals own condition, their opponents condition or a combination of the two. The use of chemical information to assess the quality of rivals has been underestimated despite its central role in the regulation of social interactions in many taxa. Here, we studied pairwise contests between founding queens of the ant Lasius niger to investigate whether the decision to engage in agonistic interactions relies on self-assessment or mutual assessment. Queens modulated their aggressive behaviours depending on both their own status and their opponents status. We found no influence of lipid stores or size on the onset of fights. However, differences in cuticular chemical signatures linked to fertility status accurately predicted the probability of behaving aggressively in pairs. Our study thus suggests that ant queens could rely on mutual assessment via chemical cues to make informed decisions about fight initiation. Summary: Lasius niger ant queens compare their own status of fertility with that of their rivals before deciding whether to engage in lethal interactions.