The intracellular symbiont Wolbachia enhances recombination in a dose-dependent manner

Wolbachia pipientis is an intracellular alphaproteobacterium that infects 40-60% of insect species and is well known for host reproductive manipulations. Although Wolbachia are primarily maternally transmitted, evidence of horizontal transmission can be found in incongruent host-symbiont phylogenies and recent acquisitions of the same Wolbachia strain by distantly related species. Parasitoids and predator-prey interactions may indeed facilitate the transfer of Wolbachia between insect lineages but it is likely that Wolbachia are acquired via introgression in many cases. Many hypotheses exist as to explain Wolbachia prevalence and penetrance such as nutritional supplementation, protection from parasites, protection from viruses, or straight up reproductive parasitism. Using classical genetics we show that Wolbachia increase recombination in infected lineages across two genomic intervals. This increase in recombination is titer dependent as the w MelPop variant, which infects at higher load in Drosophila melanogaster , increases recombination 5% more than the w Mel variant. In addition, we also show that Spiroplasma poulsonii , the other bacterial intracellular symbiont of Drosophila melanogaster , does not induce an increase in recombination. Our results suggest that Wolbachia infection specifically alters host recombination landscape in a dose dependent manner. Article Summary The ubiquitous bacterial symbiont Wolbachia is known to alter host reproduction through manipulation of host cell biology, protect from pathogens, and supplement host nutrition. In this work we show that Wolbachia specifically increases host recombination in a dose dependent manner. Flies harboring Wolbachia exhibit elevated rates of recombination across the 2 nd and X chromosomes and this increase is proportional to their Wolbachia load. In contrast, another intracellular symbiont, Spiroplasma , does not lead to an increase in recombination across the intervals tested. Our results point to a specific effect of Wolbachia infection that may have a significant effect on infected insect populations.