Influence of oxidative homeostasis on bacterial density and cost of infection in Drosophila–Wolbachia symbioses
Abstract
The evolution of symbioses along the continuum between parasitism and mutualism can be influenced by the oxidative homeostasis, that is the bal- ance between reactive oxygen species (ROS) and antioxidant molecules. Indeed, ROS can contribute to the host immune defence to regulate sym- biont populations, but are also toxic. This interplay between ROS and sym- biosis is notably exemplified by recent results in arthropod–Wolbachia interactions. Wolbachia are symbiotic bacteria involved in a wide range of interactions with their arthropods hosts, from facultative, parasitic associa- tions to obligatory, mutualistic ones. In this study, we used Drosophila–Wol- bachia associations to determine whether the oxidative homeostasis plays a role in explaining the differences between phenotypically distinct arthro- pod–Wolbachia symbioses. We used Drosophila lines with different Wolbachia infections and measured the effects of pro-oxidant (paraquat) and antioxi- dant (glutathione) treatments on the Wolbachia density and the host sur- vival. We show that experimental manipulations of the oxidative homeostasis can reduce the cost of the infection through its effect on Wol- bachia density. We discuss the implication of this result from an evolution- ary perspective and argue that the oxidative homeostasis could underlie the evolution of tolerance and dependence on Wolbachia.