Effects of Wolbachia infection on fitness-related traits in Drosophila melanogaster

Wolbachia is an intracellular symbiont that infects a large number of arthropod species, ensuring its success in populations by influencing host reproduction. The w Mel strain in Drosophila melanogaster does not cause any strong modifications of sexual reproduction. Consequently, it is not clear how the high infection rates of the bacterium in populations of this species are maintained. The w Mel strain is classified into two groups of genotypes - w Mel and w MelCS. The w Mel genotype is ubiquitous in populations, while w MelCS is rare. In this study, we analyzed fitness-related traits in isofemale lines from the unique natural population from Uman (Central Ukraine), in which we observed preservation of the rare w MelCS genotype despite the fluctuations of infection rates between years. We analyzed these effects of Wolbachia genotype and host genetic background on important fitness parameters such as sensitivity to cold and oxidative stress, female fecundity and lifespan. We found that, in the studied population, Wolbachia had an impact on fitness traits only in certain Drosophila genotypes. Positive effects were manifested in the alterations of fecundity, but at the cost of reduced lifespan and resistance to stress. Based on these findings, we conclude that the effect of bacteria on fitness and stress related traits is context-dependent and is modified by the host genotype, at least in the lines established from the Uman population.