Evolution of endosymbiotic Wolbachia bacteria across different hosts

Wolbachia is an intracellular bacterium that is mainly transmitted vertically from mother to offspring, although evidence exists for occasional horizontal transfer even between unrelated host species. To explore these evolutionary dynamics in detail, we expanded the number of known Wolbachia genomes by screening over 30,000 publicly available shotgun sequencing data from more than 500 arthropod and nematode species. By assembling over 1000 of high quality genomes, we provide a large-scale collection of Wolbachia genomes that substantially increases host representation. Here we will present our main findings published in recent articles, as well as preliminary results of ongoing investigations to estimate the origin and divergence of Wolbachia. We generated phylogenies based on both core-genome and gene content that reveal recent horizontal transfers amongst distantly related hosts. We found various instances of gene function gains and losses in different Wolbachia super-groups and in sperm–egg incompatibility inducing strains which might indicate distinct selective pressure in different hosts. Overall, our results suggest that the diversity and the evolutionary history of Wolbachia are driven by a combination of horizontal transmission and adaptation to the host.