Long-Term Measures of Climate Unpredictability Shape the Avian Endocrine Stress Axis

Area of Science:

• Endocrinology
• Ecology
• Evolutionary Biology

Background:

• The vertebrate stress response, mediated by glucocorticoids, is crucial for adapting to environmental changes.
• Glucocorticoids are plastic but also subject to ecological selection, yet how timescales of environmental variation influence them is unclear.

Purpose of the Study:

• To investigate how precipitation variation across different timescales (months, years, decades) shapes glucocorticoid response components in superb starlings.

Main Methods:

• Intraspecific comparative study of superb starlings across eight Kenyan sites over multiple years with varying precipitation.
• Assessed baseline and stress-induced glucocorticoid levels.
• Quantified adrenal sensitivity using adrenocorticotropic hormone injections.

Main Results:

• Baseline glucocorticoid levels were influenced by both short- and long-term precipitation.
• Stress-induced glucocorticoid levels were not well explained by precipitation on any timescale.
• Adrenal sensitivity was highest in unpredictable environments and shaped by long-term precipitation.

Conclusions:

• Glucocorticoid variation is best explained by environmental variation beyond individual lifespans, with baseline levels also reflecting short-term conditions.
• Long-term precipitation patterns may act as a microevolutionary pressure on the endocrine stress axis, influencing adaptation to environmental change.