Social Hymenoptera (wasps, ants, bees) possess a unique mode of reproduction. Typically, males produce the total amount of their spermatozoa during the nymphal phase solely from the energy reserves acquired during the larval phase. When the adult male hatches, the testes regress and the spermatozoa are then stored in their seminal vesicles. Mating takes place during a mating flight in which hundreds of males and females from surrounding colonies participate only once in their life. Sperm cells are transmitted during mating and are stored in the queen's spermatheca for the rest of its life (which can last several decades depending on the species). After mating, the male dies and the queen founds a new colony from the sperm received during the nuptial flight. She will never re-mate again and will use parsimoniously the spermatozoa to fertilize her eggs. Several factors are likely to dammage sperm cells, among them nutritional deficiencies during development, pathogens transmitted during mating or the immune defenses of the female that hosts sperm. Yet these sperm cells are extremly valuable because they are not renewable, and the queen will use them throughout her whole life to maintain a sufficient working force ensuring all the functions of the colony. The reproductive success of both males and females is highly dependent on the protection and maintain of spermatozoa.In this work we studied different factors that can affect the quantity, quality and protection of sperm in ants. The focus was made at three different stages: during the production of sperm cells, during their transmission at the time of mating and during their storage in the queen’s spermatheca. First, we showed that the investment in somatic development and in sperm quality take precedence over the production of large quantities of sperm cells. Second, we tested the presence and activity of two major components of the immune system (phenoloxidase system and antibacterial substances) in the sexual organs of virgin and mated ants, and we show that sperm protection uses specific systems which response is variable over time. In addition, we studed the temporal variations of these immune responses in the general insect system before and after mating. Finally, we examine the bacterial abundances and communities present in the reproductive organs at these same periods. We show the presence of some bacterial groups from the sperm storage organs that could play a role in the maintenance of spermatozoa. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished