The Effects of Timed Exogenous Corticosterone Exposure on Batrachochytrium dendrobatidis Infection Load in Plethodon cinereus

Book, Halle

The Effects of Timed Exogenous Corticosterone Exposure on Batrachochytrium dendrobatidis Infection Load in Plethodon cinereus

Persistent URL

https://hdl.handle.net/10456/59122

Author(s)

Book, Halle

Date Issued

April 1, 2025

Abstract

Stress responses in vertebrates often involve physiological changes mediated by glucocorticoids (GCs), such as cortisol in mammals and corticosterone (CORT) in amphibians. These hormones, produced by the adrenal cortex in response to hypothalamic-pituitary-adrenal axis activation, are key to an organism's stress response. The primary function of GCs is to modulate the stress response, ensuring that the organism can handle stressors and maintain homeostasis. In addition to the energetic effects that CORT has on homeostasis, it can have varying effects on immunity that fluctuate with time and timing of exposure. When chronically elevated, CORT can decrease immunity; when acutely elevated, CORT can have positive or negative effects on immunity. Because of this, acute elevations could have different consequences if they are acutely increased before, or, after pathogen exposure. If acutely elevated before pathogen exposure, CORT can prime the immune system but also create vulnerabilities that increase susceptibility. While increased CORT levels can prepare the body to face immediate stressors by mobilizing resources such as energy and immune cells, if these resources deplete too quickly or immune cell balance is disrupted, the immune system is ultimately less prepared for pathogen invasion. If acutely elevated after pathogen exposure, CORT can suppress the immune system’s ability to combat the infection effectively. CORT levels rise and prioritize energy for survival over immune function which can leave organisms more susceptible to pathogen invasion. This study investigates the interaction between CORT elevation, Batrachochytrium dendrobatidis (Bd) exposure, and infection load in red-backed salamanders (Plethodon cinereus). Bd, a pathogenic fungus, disrupts ion and water balance through infection of the skin and is responsible for significant amphibian declines. Using differently timed acute CORT elevations, this research explored how variations in CORT levels affect Bd susceptibility and infection load. I hypothesized that the timing of CORT elevation, particularly one day prior to Bd exposure, will lead to the highest infection burden and greater mass changes because stressors induced one day prior to infection will be the most important time as the organism’s immune function is weakened. I discovered significant differences in the timing of CORT application on the infection prevalence and percent mass change. Although infection prevalence varied between treatment groups, we are unable to identify which treatment groups differ from one another. All treatments that received CORT decreased in mass while the control group increased in mass. Conversely, the timing of CORT application was not found to have a significant difference on infection load. My study added to the literature significantly as the timing of stress in relation to pathogen exposure has not been researched on this level. Therefore, more studies are needed to understand the timing of CORT exposure and its impact on organisms to fully comprehend the relationship between different timed stressors and the overall Bd infection load of red-backed salamanders.

Major

Biology

Honors

Biology, 2025

First Reader(s)

Venesky, Matthew D.