Abstract
Current life history theory suggests that the allocation of energetic resources between competing physiological needs should be dictated by an individual’s longevity and pace of life. One key physiological pathway likely to contribute to the partitioning of resources is the vertebrate stress response. By increasing circulating glucocorticoids the stress response can exert a suite of physiological effects, such as altering immune function. We investigated the effects of stress physiology on individual immunity, reproduction and oxidative stress, across an urban landscape. We sampled populations in and around St. George, Utah, examining corticosterone in response to restraint stress, two innate immune measures, reproductive output, and the presence of both reactive oxygen metabolites and antioxidant binding capacity, in populations of common side-blotched lizards (Uta stansburiana) experiencing variable levels of environmental stress. Additionally, using capture-mark-recapture techniques, we examined the relationships between these physiological parameters and population-level differences. Our results reveal elevated physiological stress corresponds with suppressed immunity and increased oxidative stress. Interestingly, urban populations experiencing the most physiological stress also exhibited greater reproductive output and decreased survival relative to rural populations experiencing less physiological stress, demonstrating a tradeoff between reproduction and life maintenance processes. Our results suggest that environmental stress may augment life history strategy in this fast-paced species, and that shifts in life history strategy can in turn affect the population at large. Finally, the urban environment poses definite challenges for organisms, and while it appears that side-blotched lizards are adjusting physiologically, it is unknown what fitness costs these physiological adjustments accrue.
Highlights
A major challenge in biology is the understanding of how organisms distribute limited resources among physiological processes
Because no differences in baseline CORT concentration were detected across populations, only CORT response was included in the analysis
Because individuals were sampled across three months, and month is correlated with female reproductive stage and is known to correspond with male breeding condition, month of sampling was included in the General Linear Models (GLM) analysis as a second level temporal effect and an indirect measure of reproductive state
Summary
A major challenge in biology is the understanding of how organisms distribute limited resources among physiological processes. Reproductive processes limit available resources and thereby influence their allocation among competing mechanisms necessary for an organism’s survival and maintenance [4], [8,9,10]. Immune function is a key aspect of individual self-maintenance, because it is necessary for effective response to disease and parasites, and is vital for survival [14,15]. Due to the high energetic cost of coping with infections, immunity can limit resource availability for other processes, including reproduction, thereby potentially decreasing an individual’s fitness [16]. The stress response and corresponding glucocorticoid (GC) release are known to affect virtually all aspects of immune function [17,18] critical to self-maintenance. Increased physiological stress is related to the overproduction of reactive oxygen metabolites, and without sufficient ability to clear those metabolites, can have direct deleterious effects on tissues and survival [19,20]
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