Wolbachia in natural Drosophila simulans (Diptera: Drosophilidae) populations in Ukraine

In Drosophila , endosymbiotic bacteria Wolbachia were first described in the late 1980s as a bacterial agent causing cytoplasmic incompatibility in Drosophila simulans . Since then, Wolbachia have been monitored regularly in American and Australian natural populations of these species. Based on differences in the bacteria’s prevalence in these populations, two models for description of mechanisms of infection frequencies dynamics were proposed – bistable and Fisherian waves. To date, the information about Wolbachia ’s prevalence and effects in European populations of flies has been limited. The dynamics of infection rates in populations, mobile element activity, adaptive changes and the interplay of this factors in flies that are on their way to colonize new habitats are of great interest, especially in the context of global climate change causing range expansion in many species. D. simulans is in the process of colonizing territory in Ukraine. This provides a unique opportunity to investigate the evolution of new adaptations in real time during range expansion and climate change. Here, we report high levels of Wolbachia infection frequencies for several years in D. simulans population from Odesa. Using whole genome sequencing we show that the Wolbachia from individuals from this population belong to the w Ri strain. We show that the relative density of Wolbachia varies in different individuals, and identified 3,394 variable positions in 6 Wolbachia genomes, suggesting low diversity in Wolbachia in this population. We investigated two phenotypic traits that were putatively adaptive occurring in natural populations of D. simulans – diapauses and gonadal dysgenesis. We find that being infected with Wolbachia does not affect a fly’s diapause phenotype in three D. simulans genetic backgrounds and contradictory results in one strain. We also find that Wolbachia appears to enhance gonadal dysgenesis in crosses to determine dysgenesis-inducing ability. These results may suggest that Wolbachia promote P -element or other transposable element activity.