Hormonal and Behavioral Responses to Environmental Changes

Hormonal Response to Environmental Change

• Hormones are influenced by both social and ecological factors:
  • Ecological factors: Food availability, severe weather, presence of predators.
  • Social factors: Interactions with other organisms.
• Glucocorticoids:
  • Often called "stress hormones."
  • Play essential roles in metabolism, immune function, and physiological processes.
  • Enable rapid responses to stressors through behavioral and physiological adjustments.

Biological Response to Predation

• Presence of hawk triggers:
  • Energy diversion to flight muscles.
  • Increased blood flow and cardiovascular enhancement.
  • Cognitive changes in sparrows, mediated by catecholamines (noradrenaline and adrenaline).
• Effects of glucocorticoids are rapid, occurring within seconds to minutes.

Physiological Responses to Severe Weather

• Example: Spring snowstorm triggers:
  • Immune system engagement.
  • Inhibition of reproductive physiology and behavior.
  • Decreased appetite, return to nonbreeding activities (e.g., foraging, nestbuilding).

HPA Axis Stress Response

• Hypothalamic-Pituitary-Adrenal (HPA) Axis regulates stress response:
  • Periventricular hypothalamus secretes corticotropin-releasing hormone (CRH) into portal circulation.
  • Adrenocorticotropin (ACTH) is released into circulation, stimulating cortisol release from adrenal cortex.
  • Cortisol inhibits CRH release, creating a feedback loop (questioning its name).

Understanding Stress Effects

• Stress can be classified as:
  • Acute stress: Short-term, can be beneficial.
  • Chronic stress: Long-term, potentially harmful (brain damage, cell death, premature aging).
• Glucocorticoids can be adaptive short-term but maladaptive long-term if chronic stress persists.

Glucocorticoids and Environmental Change

• High levels of glucocorticoids may promote plastic behavioral responses to environmental changes.
• Example: House sparrows’ range expansion along Kenya’s coast:
  • Birds farther from the introduction site showed greater exploratory behavior and stronger stress responses.

Social Stress Responses

• In high population density or territorial intrusions, glucocorticoid levels rise across vertebrates (mammals, birds, fish, reptiles).
• In social species, the relationship between dominance rank and glucocorticoids depends on:
  • Hierarchy stability.
  • Methods of gaining and maintaining dominance.

Reproductive Dynamics in Meerkats

• In cooperatively breeding meerkats:
  • Dominant females suppress reproduction in subordinates, leading to increased glucocorticoids and reduced reproductive success.

Antipredator Behavior Overview

• Antipredator strategies include:
  • Active defense (attacking or deterring predators).
  • Strategies involve solitary or group approaches.
• Costs of social defenses might include resource competition or increased visibility to predators.

Cryptic Coloration and Survival Strategies

• Cryptic coloration adapts based on habitat (e.g., Biston betularia prefers shading near limb joints).
• Experimental evidence shows birds find cryptically colored moths on appropriate backgrounds less often.

Behavioral Adaptations to Predation

• Certain moth species make perch choices based on predation risk (e.g., Catocala relicta on white birch).
• Research indicates effective camouflage can significantly enhance survival.

Warning Coloration and Mimicry

• Aposematic coloration: Warns predators about an organism’s unpalatability.
• Batesian mimicry: Edible species mimic distasteful ones.
• Müllerian mimicry: Multiple distasteful species evolve similar warning coloration.

Stotting Behavior in Gazelles

• Stotting: An escape strategy where gazelles signal they are aware of predators and capable of fleeing.
• This behavior affects predator hunting success, particularly against cheetahs.

Lizard Display Behavior

• Push-up displays may indicate a lizard’s health and fitness level, correlated with stamina under threat.