The role of prooxidants and antioxidants in shaping life-history and parasite tolerance in Anopheles mosquitoes

Oxidative homeostasis plays important roles in physiology, for reactive oxygen species not only lead to damaging oxidative stress, but also regulate important physiological processes like immunity and longevity. ROS are therefore expected to be a key factor underlying many host-parasite interactions. We evaluated the role of the host’s oxidative status on the outcome of infection with the mosquito Anopheles gambiae infected by the microsporidian Vavraia culicis . To do so, we manipulated the oxidative status of the mosquitoes by feeding them early (the first four days after emergence) or late (from five days after emergence onwards) either a standard sugar source or one supplemented with a prooxidant (hydrogen peroxide) or antioxidant (vitamin C), and then measured the longevity and fecundity of uninfected and infected mosquitoes and (for infected mosquitoes) the parasite load at a given day (13 days after emergence) or when the mosquitoes died. The prooxidant generally increased longevity, but if consumed early after emergence its impact was lessened by the infection by Vavraia . In contrast the antioxidant increased fecundity, and the impact was not affected by the status of infection or by the timing of consumption. Finally, early consumption of both supplements increased Vavraia ’s spore load at 13 days after emergence and at death. In contrast, late consumption enhanced the parasite’s growth late in the mosquito’s life. Thus, our experiment revealed complex effects of prooxidant and antioxidant consumption, emphasising the critical role of timing and context in shaping their influence on biological traits.