Phylogenetic evidence for horizontal transmission of Wolbachia in host- parasitoid associations

TLDR

Wolbachia are endosymbiotic bacteria that infect many arthropods, alter reproduction, and exhibit phylogenies that do not mirror their hosts, implying frequent horizontal transmission. The study investigates horizontal Wolbachia transfer in host–parasitoid systems, focusing on hymenopteran parasitoids of frugivorous Drosophila. Phylogenetic relationships of Wolbachia strains were inferred from the highly variable wsp gene across parasitoid and host species. We found that four of five common European Drosophila parasitoid species carry Wolbachia, often with multiple infections, and that their Wolbachia variants closely resemble those of their hosts, supporting frequent natural horizontal transfer.

Abstract

Endosymbiotic Wolbachia infect a number of arthropod species in which they can affect the reproductive system. While maternally transmitted, unlike mitochondria their molecular phylogeny does not parallel that of their hosts. This strongly suggests horizontal transmission among species, the mechanisms of which remain unknown. Such transfers require intimate between-species relationships, and thus host-parasite associations are outstandingly appropriate for study. Here, we demonstrate that hymenopteran parasitoids of frugivorous Drosophila species are especially susceptible to Wolbachia infection. Of the five common European species, four proved to be infected; furthermore, multiple infections are common, with one species being doubly infected and two triply infected (first report). Phylogenetic statuses of the Wolbachia infecting the different species of the community have been studied using the gene wsp, a highly variable gene recently described. This study reveals exciting similarities between the Wolbachia variants found in parasitoids and their hosts. These arguments strongly support the hypothesis of frequent natural Wolbachia transfers into other species and open a new field for genetic exchanges among species, especially in host-parasitoid associations.