The bilharziasis is a human parasitic disease which is in the second world rank, after the malaria, in terms of morbidity and mortality inferred by the parasite. More than 200 million people are infested in 74 countries and more than 200 000 people die a year (Chitsulo and al. 2004; Gryseels and al. 2006). Schistosoma mansoni, here studied, is responsible for the intestinal bilharziasis. This parasite possesses a complex life cycle, getting through necessarily two hosts: an intermediate host mollusk of fresh water and a human definitive host or murin. During the cycle of development, the various stages are exposed to diverse environments. For example, the embryonic stages can be confronted with several intermediate hosts (origin of mollusk) or definitive (human being or murin). My thesis research concerns the influence of the environment on the épigénome of Schistosoma mansoni. The epigenetic information is an additional source for the creation of variants phenotypic, we propose that some of these variants can be inherited and selected, and so confer an advantage to the parasite. To invest this hypothesis we decided to modify the environment of the parasite of a way biotick and abiotique, when it develops within the definitive host or when it is for the contact of the intermediate host. Indeed, Schistosoma mansoni is an endoparasite thus every host, in whom he is going to remain, represents its direct environment. For it we used a drug anti-helminthe and an intermediate host allopatrique. The answer of the parasite to the various changes of environments was analyzed by the population (milked by life history) in the molecule (genome, épigénome, transcriptome). The new techniques of molecular biology and massive sequencing allowed us to realize global studies. During this thesis research, the various experimental evolutions led to two riddles: (1) " Fast Adaptation of Schistosoma mansoni to a drug anti-helminthes " and (2) " Fast Adaptation of Schistosoma mansoni to South America ". The results obtained for the latter brought the third riddle: (3) " Sexual Differentiation in the absence of gene W-spécifique in a system ZW "!
