Wolbachia are the most widespread endosymbiotic bacteria in animals.In many arthropod host species,they manipulate reproduction via several mechanisms that favor their maternal transmis-sion to offspring.Among them,cytoplasmic incompatibility (CI) promotes the spread of the sym-biont by specifically decreasing the fertility of crosses involving infected males and uninfected females,via embryo mortality.These differences in reproductive efficiency may select for the avoidance of incompatible mating,a process called reinforcement,and thus contribute to popula-tion divergence.In the terrestrial isopod Porcellio dilatatus,the Wolbachia wPet strain infecting the subspecies P.d.petiti induces unidirectional CI with uninfected individuals of the subspecies P.d.dilatatus.To study the consequences of CI on P.d.dilatatus and P.d.petiti hybridization,mitochon-drial haplotypes and Wolbachia infection dynamics,we used population cages seeded with differ-ent proportions of the 2 subspecies in which we monitored these genetic parameters 5 and 7 years after the initial setup.Analysis of microsatellite markers allowed evaluating the degree of hybridiza-tion between individuals of the 2 subspecies.These markers revealed an increase in P.d.dilatatus nuclear genetic signature in all mixed cages,reflecting an asymmetry in hybridization.Hybridization led to the introgressive acquisition of Wolbachia and mitochondrial haplotype from P.d.petiti into nuclear genomes dominated by alleles of P.d.dilatatus.We discuss these results with regards to Wolbachia effects on their host (CI and putative fitness cost),and to a possible re-inforcement that may have led to assortative mating,as possible factors contributing to the observed results.