Phylogenetic status of a fecundity-enhancing Wolbachia that does not induce thelytoky in Trichogramma.

Wolbachia are widespread bacteria which infect a number of species of insects and other arthropods. They manipulate the reproduction of their hosts at their own advantage. In Trichogramma species all Wolbachia known so far induce thelytoky and form a monophyletic group in the B subdivision of Wolbachia. Here we show that some strains of the arrhenotokous species Trichogramma bourarachae harbour Wolbachia symbionts that locate in the A subdivision, and which do not induce thelytoky. Although the symbiont of T. bourarachae is closely related to Wolbachia that induce cytoplasmic incompatibility in other insects, no cytoplasmic incompatibilities were found in crosses involving infected and uninfected strains. In T. bourarachae the presence of this Wolbachia is associated with a higher fecundity of strains. Our results strongly suggest that Wolbachia are involved in this increased fecundity. Theoretical models on the evolution of host-Wolbachia interaction predict that a reduced effect on reproduction can be selected for if cost of infection is reduced. The effect in T. bourarachae should illustrate this prediction.