Understanding Wolbachia acquisition and co-divergence of hosts and their associated bacteria: Wolbachia infection in the Chorthippus parallelus hybrid zone
Wolbachia is one of the best known bacterial endosymbionts affecting insects and nematodes. It is estimated that it infects 40% of insect species, so epidemiologically it may be considered a pandemic species. However, the mechanisms by which it is acquired from other species (horizontal transmission) or by which it coevolves with its hosts as a result of vertical transmission across generations are not known in detail. In fact, there are few systems in which the codivergence between host and bacterium has been described. This study goes in deep in the Wolbachia infection in the grasshopper Chorthippus parallelus. This well-known system allows us to investigate the mechanism of acquisition of various Wolbachia strains in a new host, and the bacterial genomic changes during bacterial-host codivergence: We describe the genetic diversity of Wolbachia strains infecting both subspecies of C. parallelus and analyse their phylogenetic relationship. We also show the emergence of new bacterial alleles resulting from recombination events in Wolbachia infecting hybrid hosts. Our data suggest that F strains detected in this grasshopper have co-diverged with its host, versus a more recent horizontal transmission of B strains. According with this, we discuss the potential role of Wolbachia in the dynamics of the grasshopper hybrid zone and in the divergence of the two grasshopper subspecies since the origin of their hybrid zone.