Recombination confounds interpretations of Wolbachia evolution

Wolbachia are vertically transmitted bacteria known from arthropods and nem atode worms, which are maintained in host populations because they either p hysiologically benefit infected individuals or parasitically manipulate the ir reproduction. The different manipulation phenotypes are scattered across the Wolbachia phylogeny, suggesting that there have been multiple evolutio ns of similar phenotypes. This conclusion relies on the assumption of an ab sence of recombination between bacterial strains, so that the gene used to reconstruct the phylogeny reflects the evolutionary history of the genes in volved in the trait. We tested for recombination by reconstructing the phyl ogeny of two Wolbachia genes from seven B-subdivision strains. The two gene s produced mutually incompatible topologies, indicating that these lineages are subject to genetic recombination. This means that many evolutionary pa tterns inferred from Wolbachia phylogenies must be re-evaluated. Furthermor e, recombination may be an important feature both in the evolution of the m anipulation phenotypes and avoidance of Mullers' ratchet. Finally, we discu ss the implications of recombinations for attempts to genetically engineer Wolbachia for use in the control of crop pests and human pathogens.