Phylogénie Et Evolution Du Comportement Social Chez Les Blattes ...

Ab s t r a c tPh y l o g e n y a n d e v o l u t i o n o f s o c i a l b e h av i o u r in c o c k r o a c h e s a n dt e r m i t e sThe evolution of social behaviour has been studied in cockroaches and termites(Insecta: Dictyoptera) with a phylogenetic approach. These two groups showa high diversity of social behaviours and can be used to study three importantevolutionary transitions. First, the shift from a gregarious toward a solitary way of life shouldprovide the opportunity to understand the behavioural changes occurring with basic socialhabits. The second transition - gregarism toward subsociality – should shed light on theestablishment of social relationships between individuals of a same family (the parents andtheir brood). The subfamily Zetoborinae has been used to study the evolutionary factorswhich could have driven each of these two first transitions. The third transition studied withintermites deals with the origin of workers castes and involves “altruistic” behaviours, the originof which has given rise to many theoretical developments.In a first step, the phylogenies of these groups have been inferred using several data sets.Large portions of the genes 12S, 16S, 18S, 28S, COI, COII and Cytb have been sequenced for90 species (i.e. 7000 bp for each species). Morphological and behavioural data for cockroachesand developmental data for termites have also been included in the phylogenetic analyses.We have proposed several new methodologies to analyse non-traditional characters, such asbehaviour and development. They have been defined in a more accurate way by consideringthe sequences in which they take place. The analyses have been carried out either by directoptimization of stereotyped sequences, or by using a modified event-pairing approach in thecase of non-stereotyped sequences.In a second step, the results of the phylogenetic analyses have been used to study theevolutionary transitions in social behaviour. Few behavioural changes within the repertoiresor the behavioural sequences occurred during the transition gregarism-solitary life habits,which would suggest the occurrence of a strong phylogenetic inertia. Regarding the secondtransition, subsociality has not evolved by using “gregarism-like” behavioural sequences inanother context, even though the ancestral tolerance to conspecifics has remained the same.Finally, the study of developmental sequences in termites showed that the “true” workerscaste evolved three times by convergence and parallelism. A decrease in the developmentalflexibility has also been documented in relationship with the foraging behaviours of workers.The adaptive value of worker castes is corroborated even if the nature of the selection involvedremains to be discovered.