Warmer Temperature and Aging Interact to Shape how Mosquitoes Survive and Respond to Infection

Abstract

Insect physiology is shaped by factors inherent to the environment, such as temperature, and factors inherent to the insect, such as age. As poikilotherms and ectotherms, the body temperature of most insects is predicated by the temperature of the environment. Global temperatures are warming, which is quickening insect development, raising metabolism, and altering the response to infection. Moreover, as insects age, they senesce, causing their body to deteriorate and immune function to weaken. An organism’s age is measured by time alive (chronological age) and by how well their body functions (physiological age). In homeotherms, these processes are linked. In poikilotherms, these processes may become unlinked by changes in temperature. Using the African malaria mosquito, Anopheles gambiae, I evaluated whether warmer temperature alters the progression of senescence. I hypothesized that mosquitoes age faster physiologically when the temperature is warmer, which may have implications for their competency as disease vectors. To test this, I investigated the effects of warmer temperature and aging in tandem and assessed changes in body size and composition, survival, and immune function. I demonstrate that warmer temperature and aging interact to affect many facets of mosquito physiology. Both the aging-dependent decrease in protein content and survival occur earlier in life when the temperature is warmer. Moreover, the aging-dependent increase in infection intensity occurs earlier in life when the temperature is warmer, indicating that a mosquito’s general ability to control a systemic infection declines at a faster rate when the temperature is warmer. I further show that the strength of the cellular immune response declines with warmer temperature and aging, and that this aging-dependent decline quickens when the temperature is warmer. Thus, warmer temperature accelerates senescence, decoupling chronological and physiological age in mosquitoes. Because most insects are poikilothermic ectotherms, the interactive effects between temperature and aging should be considered when constructing models that predict the efficacy of insects as pollinators, agricultural pests, and disease vectors in our warming world.