Wolbachia infection dynamics in evolving Drosophila populations

The infection dynamics of endosymbiont Wolbachia is complex, resulting substantial differences between populations, seasons as well as between strains. The causes of these heterogeneities are not yet understood, partly due to the complexity of natural environments. Preparatory work showed that experimental evolution of a Portuguese D. melanogaster population uncovered environment-specific fitness differences among Wolbachia strains. Based on these results, this proposal aims to characterize the dynamics of Wolbachia infection in different environments. Using whole genome sequencing in combination with SNP genotyping the trajectories of different Wolbachia strains will be followed and their relative fitness will be determined. To shed light on the habitat-specific dynamics, a range of Wolbachia strains will be tested for different fitness parameters in a common genetic background. It is anticipated that the results obtained during this project will have profound impact on the understanding of Wolbachia dynamics in natural populations.

Wolbachia is an intracellular bacterium with a broad range of consequences on its host. In this project, we studied the influence of C virus infection on Wolbachia dynamics in Drosophila melanogaster. Our analyses confirmed that Wolbachia protects its host against Drosophila C virus infection. Of particular relevance to this project was the observation that the degree of protection differs between Wolbachia strains. The same Wolbachia strain that increased during cold temperature treatment also increased during C virus exposure. In combination with the long-term dynamics of Wolbachia in hot environments, where the same Wolbachia strain from clade V increased in frequency during later generations we needed to reconsider the interpretation that the spread of the Wolbachia strain is a direct effect of temperature. Rather, we propose that these dynamics are best explained by different C virus load in the hot and cold environments. Interestingly, we could also show that the Drosophila host can develop similar C virus resistance levels in the absence of Wolbachia as the one observed in Wolbachia infected flies.