Biology- Is All Stress the Same? Characterizing the Response to Superficially Similar Stressors in Western Fence Lizards.

Abstract

Stress is a ubiquitous aspect of life, and its effects on physiological processes have been extensively studied in various animal species. In reptiles, stress can activate the hypothalamic pituitary-adrenal (HPA) axis, which leads to the release of corticosterone (CORT). CORT is a hormone that helps the organism respond to environmental stressors by increasing glucose availability, which plays a key role in the regulation of metabolism and immune function. I hypothesized that the stressors are inducing different stress responses based on the observed metabolic rate and that CORT is driving these differences based on the results of a previous study where stressors affected metabolic rates in a lizard. I examined the stress response in western fence lizards (Sceloporus occidentalis) under predator-threat stressor treatments such as running them to exhaustion, chasing them with a remote-controlled robot (Humbug), injecting them with adrenocorticotropic hormone (ACTH), and control (normal conditions). I tested the impact of stress on the lizards’ energetics, plasma circulating CORT, and respiration rate. I measured plasma CORT levels using an enzyme immunoassay (EIA), and I measured recovery respiration rate using flow-through respirometry. I did not observe the same metabolic response as observed previously, as the stressor treatment did not induce different recovery respiration rates. The ACTH treatment increased CORT concentrations and blood glucose the most in comparison to the other treatments. In the future, examining differential gene expression with the help of RNA-seq analysis can help us understand key genes responsible for the physiological changes observed in CORT levels and its associated effects in the western fence lizard.