Student Research Projects - Biology
Title of Project
Investigating Temporal Variation in the Stress Response and Protein Catabolism of the Northern Cardinal (Cardinalis cardinalis)
The glucocorticoid stress response is designed to respond to extended, long-term threats, such as predators and environmental changes, in order to ensure the survival of an animal. The catecholamines of the adrenal medulla (i.e. epinephrine and norepinephrine) are an integral part of the fight or flight response. These hormones are released rapidly and increase metabolic rate and vasoconstriction. Concurrently, a cascade of hormonal signals travels along the hypothalamic-pituitary-adrenal (HPA) axis translating external stimuli into a longer-term physiological response. These hormones, glucocorticoids, are released from the adrenal cortex and promote escape behavior and gluconeogenesis. The acute effects of glucocorticoids are beneficial to the organism, but long-term chronic levels can be detrimental to an organism's health and potentially lethal.
The aim of this study is to measure seasonal variation of both corticosterone, as an indicator of the stress response, and 3-methylhistidine (3-MH), as an indicator of muscle protein breakdown, in the Northern Cardinal and compare the two in search of trends. Four time periods of interest were chosen coinciding with important annual events in a cardinal's life cycle: 1) fall molt, 2) winter, 3) spring nest initiation/egg laying, and 4) summer chick rearing. Many studies have explored seasonal variation of corticosterone in birds, but corticosterone has been shown to be elevated at several different times throughout the course of the year.
While numerous studies have investigated temporal variation of corticosterone in migratory birds, few have examined variation in non-migratory birds and none have done so with the Northern Cardinal. Additionally, although a connection between increased glucocorticoids and protein breakdown has been made, little research has been done on seasonal variation of muscle protein breakdown in non-migratory birds. It is interesting to consider not only how the avian stress response and protein catabolism fluctuate seasonally, but also how the two interrelate.
Ongoing Work of Research Project
The total stress response (F=3.48, p=0.03) and baseline corticosterone levels (F=3.35, p=0.03) were determined to be significantly different between seasons. Post hoc analysis revealed that summer cardinals had a less robust total stress response and a lower starting baseline compared to spring. Analysis showed no sex differences in total (F=1.23, p=0.28) or baseline (F=1.71, p=0.20) corticosterone levels. These results show that there is significant variation in the stress response of C. cardinalis over the course of the year, particularly between spring and summer.
3-methylhistidine analysis is ongoing. Currently, we are in the process of validating a gas chromatography/mass spectroscopy method for detecting 3-MH.
Jonathan Haskins '10