Co-transmitted Wolbachia engage in niche-partitioning within host insect tissues

Wolbachia is a genus of maternally transmitted, obligate endosymbionts of insects and other arthropods. Some animals are infected with multiple Wolbachia strains, including Drosophila simulans with two strains “wHa” and “wNo”. This system provides a tractable model to examine infection dynamics between intracellular bacteria and their ecology within the host insect. We developed strain-specific qPCR primers and FiSH probes to examine the spatial and temporal changes in wHa and wNo titers within host tissues across development. Our results indicate that these two infections exhibit niche partitioning across host tissues. wHa is present at a significantly higher titer than wNo in the somatic tissue of both male and female D. simulans, while wNo is the predominant strain in ovarian tissue. Unexpectedly, the ratio of wHa to wNo in young embryos does not reflect those observed in the ovaries, but rather form a unique ratio not observed at any other time across development, indicating that two Wolbachia strains have different transmission dynamics. Finally, we developed a strategy to segregate the two Wolbachia strains into independent fly lines and find that wNo monoinfected D. simulans rapidly lose their infection within several generations. In contrast, wHa monoinfections appear stable, indicating that wNo may be dependent on wHa for effective vertical transmission. Future work aims to examine transcriptomes and Wolbachia tropisms under different infection scenarios with the goal of identifying factors that regulate coinfection.