The Adaptive Stress Response Overview

• Course: Psych 337
• Instructor: Dr. Jacinta C. Beehner
• Focus on how stress responses evolved as adaptive mechanisms.

Announcements

• Only 2 more class days left focusing on biological rhythms and affective disorders.
• Exam 3 scheduled for April 22 during class hours.
• Exam format will mirror previous exams.
• Importance of studying consistently rather than cramming.
• Extra credit options include attending an additional lecture next Tuesday.
• Students encouraged to evaluate the class for more extra credit.

Research Avenues in Biomedicine

• Two paths in stress research:
  • Adverse consequences - studies the negative effects of stress.
  • Evolutionary perspective - investigates how stress responses have adaptive benefits.
• Reference: Sapolsky, 2021.

Hypothalamic Hormones in Stress Response

• Stress response is driven by hormonal interactions involving:
  • Corticotropin-releasing hormone (CRH) - released from the hypothalamus.
  • Adrenocorticotropic hormone (ACTH) - released by the anterior pituitary.
  • Glucocorticoids (GC) - produced by the adrenal glands as a response to ACTH.
• The stress response involves feedback mechanisms with a focus on survival.

Effects of Stress Response on Life History Components

• The stress response prioritizes survival, affecting growth and reproduction:
  • Survival: Critical energy allocation to immediate survival needs.
  • Growth: Stress can inhibit growth and body repair mechanisms.
  • Example: European rabbit induced stress from capture led to weight loss despite higher mortality in stress conditions (Cabezas et al., 2007).
  • Reproduction: Stress can negatively impact reproductive success:
  • Example: Yellow baboons experience increased glucocorticoids during droughts, leading to lower ovulation and pregnancy rates (Beehner et al., 2006).

Allostatic Load

• Definition: Wear-and-tear from repeated stress responses leading to detrimental health effects (Bobba-Alves et al., 2022).

Stress Responses and Longevity

• HPA Activity and Lifespan: Baboons with higher HPA activity tended to die younger (up to 5 years earlier).
• The CORT-Fitness Hypothesis explains the correlation between cortisol levels and fitness outcomes, assessing when stress responses become maladaptive.

Parameters for Stress Response

• A properly functioning stress response should involve:
  • Low baseline glucocorticoids, quick response to stressors, and rapid return to baseline.
• Failures occur when homeostatic overload (excessive glucocorticoid exposure) or homeostatic failure (insufficient glucocorticoids) happens.

Frequency and Magnitude of Stressors

• Chronic stress affects lifespan; frequently exposed animals often show different health outcomes compared to those with negligible stress.
• It is pivotal to assess the fitness impact of stressors realistically.

Natural Disaster and HPA Responsivity Study

• El Niño Impact Study:
  • Research on white-faced capuchins in Costa Rica, focusing on hormone responses during environmental stressors.
  • Hypothesis: A good stress response would predict greater survival rates during challenging times (e.g., El Niño).

Findings from Capuchin Study

• Evidence suggested higher HPA responsivity correlated with survival likelihood.
  • No significant differences in baseline glucocorticoid levels between those that survived and those that did not.
• Emphasis on the importance of within-individual studies to understand glucocorticoid fitness consequences fully.

Future Directions in Stress Research

• More empirical research needed to adequately link glucocorticoid responses to fitness.
• Key questions include:
  • Review the HPA axis and hormone cascade during stress.
  • Discuss the concept of allostatic load and its implications on adaptations.
  • Analyze the Cort-Fitness hypothesis critically.
• Understanding the full scope of stress effects in wild animals and how to optimally compare different response mechanisms.