Are individuals consistent? Endocrine reaction norms under different ecological challenges

Area of Science:

• Physiological ecology
• Environmental change biology
• Animal behavior

Background:

• Organismal capacity for compensatory mechanisms is crucial for predicting environmental change responses.
• Individual variation in physiological plasticity is known, but its causes and consequences are unclear.
• A key question is whether individual responses (reaction norms) are consistent across different environmental challenges and over time.

Purpose of the Study:

• To quantify individual baseline glucocorticoid responses in house sparrows to sequential environmental challenges.
• To determine if these responses are consistent across different types of environmental challenges (temperature, wind speed, food unpredictability).
• To assess the repeatability of these physiological reaction norms over time.

Main Methods:

• House sparrows (Passer domesticus) were exposed to sequential manipulations of temperature, wind speed, and food unpredictability.
• Baseline corticosterone levels and body mass were measured under both control and stressor-exposed conditions.
• The study involved repeated blocks of sampling to assess repeatability across challenges and time.

Main Results:

• Individuals exhibited significant decreases in baseline corticosterone levels and increases in body mass during stressor exposure.
• These physiological responses were consistent across different environmental challenge types.
• High repeatability was observed in the intercept and slope of the baseline corticosterone reaction norm between challenges, though slope repeatability had broad intervals.

Conclusions:

• Endocrine plasticity, specifically baseline corticosterone response, is repeatable across diverse environmental challenges in house sparrows.
• Within-subject variation in corticosterone was linked to body mass changes during stress.
• Repeatable endocrine plasticity suggests it can evolve via genetic accommodation, where selection acts on genetic variation in reaction norms.