File:Allostatic overload as a key driver of pathogen spillover.webp

English: "Bats have evolved mechanisms to meet their exceptionally high energy needs under prevailing environmental conditions. A Baseline levels of energy (green) are required for basic daily activities – to fuel cells, to move around, to find food and water, and to maintain the immune system. At any given time, a certain amount of food - or energy - is available (blue+purple+green), which varies seasonally. Bats optimize their energy intake and energy expenditure, timing expensive activities like migration and reproduction (purple) to periods in which more food is available. Under normal conditions, an energetic buffer (blue) exists providing energetic wiggle room for years with poor food availability. B Perturbations in the environment, whether natural (e.g., fire in some instances) or man-made (e.g., downstream effects of global climate change, habitat destruction, etc.) increase the amount of energy needed for survival and reproduction. For example, animals may be required to travel greater distances to locate food and resting sites. Such increased exertion diminishes the energetic buffer that enables them to withstand periods of resource scarcity. C At its worst, these perturbations result in a reversal of fortune; less energy is available than the bat needs. In these conditions, or with disturbance or harassment, animals experience allostatic overload (red). This leads to suppression of immune function, and increased susceptibility to viral infection and shedding. Figure adapted, in part, from concepts in [Wingfield, J. C. et al. How birds cope physiologically and behaviourally with extreme climatic events. Philos. Trans. R. Soc. Lond. B Biol. Sci. 372, 20160140 (2017).]."