Modulation des décisions comportementales individuelles dans un contexte social – SEUILS

Individual decision processes have often been overlooked in insect societies. However, investigating the mechanisms underlying these processes allows understanding how individuals adjust to their environment and thereby adaptively satisfy their needs and the colony's. The theoretical framework of our project derives from response-threshold models describing individual decisions as 3-components processes: - Expression: What are the task-related signals' - Perception: What sensory and cognitive processes allow the evaluation of these signals' - Action: How is the decision reached' Each phase will be investigated in three contexts reflecting social complexity: social recognition, task allocation and worker reproductive decisions. We will unravel the role of internal and external factors on social insects' decisions in context. Social recognition, the first aspect, is based in insects on chemical signals. During encounters a phenotype-matching process allows comparison between perceived cues and an internal template acquired through an imprinting-like process and/or self-reference mechanisms. The actual behavioural response (rejection or not) depends on adaptive significance of the discrimination. Interestingly, adult social insects have also been proven able to learn an enemy-specific template from an alien colony, leading to a modified level of aggression. We aim at (1) characterising the template learning process in adults and (2) elucidating the decisions rules after stimulus assessment. We will assess the influence of bioamines and nutritional status (1) on template learning and (2) on the tolerance threshold value. Task allocation, the second social situation, is characterised by specialisation and behavioural flexibility which permit the workers to respond to colony needs. Among others, larvae may provide information on colony-level attributes and work demands, and adjust individual choices and task performances for both nursing and foraging. After identification of the larval signals, we will characterise the associated response threshold for each age-related task and analyse the effect of individual internal state on the response threshold. Worker reproductive decisions are the third aspect of decision processes studies. In most social insect species, the ability of workers to lay male eggs creates a potential conflict between all colony members for reproduction. The expression of this conflict depends on costs and benefits associated to the decision of reproducing or not. A new strategy has been discovered where workers parasitize conspecific colonies. We will investigate the influence of various factors on the choices available to workers. These choices are to work, to reproduce or to parasitize another colony. Experimental designs will be developed to allow detailed behavioural observations which will be aided by path analyses and behaviour recording software, as well as Radio Frequency identification (RFID) allowing large-scale individual monitoring. Signals will be analysed through gas chromatography. Extraction techniques will be developed to test biological activity of signals and to manipulate them, for example by creating fractions or mixed chemical signals to be used in bioassays. We will focus on the influence of two factors on individual decisions in our three social contexts: - Neuroendocrine factors (in particular biogenic amines) are known to influence various aspects of individual behaviour such as learning abilities and aggression. They also play a part in the regulation of task allocation, recognition processes and reproductive decisions. These factors will be quantified and manipulated at the individual and colony-level through injections, feeding and topical applications. - Nutritional factors play an important role as they influence colony health (resources and brood rearing) and individuals' physiology. They are directly linked with fitness and costs and benefits of the various behavioural responses. Their influence will be assessed by experimental manipulations of energetic resources both at colony and individual level. In conclusion, our project is at the crossroad of behavioural, cognitive and evolutionary sciences. We will focus on behavioural decision making in complex social contexts. Through an integrative approach of behaviour, we will bring new and much needed elements to understand the interplay between selective pressures and cognitive processes.