Warmer Temperature Accelerates Immune and Reproductive Senescence in the African Malaria Mosquito Anopheles gambiae

Abstract

A mosquito population can only be maintained if its members take a blood meal, survive, and reproduce. Because mosquitoes cannot use metabolism to regulate their body temperature, the efficiency of their physiological processes is dictated by the temperature of their environment. Warmer temperature quickens metabolism, weakens the immune response to infection, and decreases reproduction. Like most organisms, as mosquitoes age, they undergo senescence, which is a progressive deterioration in bodily function, including immunity and reproduction. Given that warmer temperature increases mosquito body temperature and alters the efficiency of physiological processes, I hypothesized that warmer temperature accelerates both immune and reproductive senescence. To test this hypothesis, I asked how warmer temperature and aging interact to shape immunity and reproduction in the African malaria mosquito, Anopheles gambiae. Specifically, I investigated how different temperatures (27°C, 30°C, and 32°C) shape (i) the humoral immune responses to infection and (ii) blood feeding and reproduction, in mosquitoes of different ages. In this dissertation, I demonstrate that warmer temperature accelerates the aging-dependent decline in both the melanization and lysis immune responses in bacterially infected mosquitoes, making them more susceptible to infection earlier in life. Additionally, warmer temperature accelerates an aging-dependent decline in blood feeding, fecundity and fertility, and at the warmest temperature of 32°C, females were infertile at all ages. The warming-based acceleration of immune and reproductive senescence is explained by changes in the expression of genes with immune and reproductive function, and by structural changes in both female and male reproductive tissues. These findings have important consequences for mosquito population dynamics and disease transmission risk, and they emphasize the need to holistically evaluate abiotic and biotic factors that impact vector physiology.