Stress responses are evolutionarily conserved mechanisms, allowing organisms to cope with environmental and internal challenges through the activation of the hypothalamic pituitary adrenal (HPA) axis and subsequent release of glucocorticoid hormones. In many small animals, including deer mice (Peromyscus leucopus), corticosterone is the primary glucocorticoid used to assess both acute and chronic physiological stress. While acute stress responses are typically flexible and short lived, chronic stress that results from prolonged activation of the HPA axis can lead to physiological dysfunction including behavioral changes and reduced fitness. In particular, reproduction is a period of chronic stress and heightened energetic demand due to the metabolic and behavioral costs associated with gestation, lactation, and parental care. This research investigates the contributions of reproductive status and environmental factors, such as habitat and density, to variation in corticosterone levels. Forty fecal samples derived from a wild population of deer mice located in the Long Island Pine Barrens were quantified for corticosterone using an ELISA hormone assay. I hypothesized that pregnant female deer mice exhibit higher corticosterone levels than nonpregnant females and males due to the sustained metabolic demands of reproduction. Alternatively, local environmental conditions such as population density, food availability and seasonal variation may play a larger role in determining corticosterone levels. Corticosterone assays are in progress and will contribute to understanding how internal and environmental stressors shape both individual fitness levels and population dynamics within wild mammal populations.
Acknowledgements: SRG