Urinary Cortisol Increases During a Respiratory Outbreak in Wild Chimpanzees

Area of Science:

• Primate endocrinology
• Wildlife immunology
• Stress physiology

Background:

• Cortisol is key in mammalian stress response but can suppress immunity.
• Sickness behaviors may conserve energy during costly immune responses.
• Endocrinological correlates of sickness are understudied, especially in wild primates.

Purpose of the Study:

• Investigate cortisol's role in immune response and sickness behavior in wild chimpanzees.
• Examine the relationship between cortisol and immune activation markers during a disease outbreak.
• Understand the energetic costs of immune defense in a natural environment.

Main Methods:

• Measured urinary cortisol and neopterin levels in wild chimpanzees before, during, and after a respiratory disease outbreak.
• Utilized liquid chromatography-mass spectrometry for precise hormone and biomarker quantification.
• Correlated changes in cortisol with immune activation (neopterin) and disease status.

Main Results:

• Urinary cortisol levels were over 10-fold higher during the outbreak compared to baseline.
• Elevated cortisol levels correlated positively with increased neopterin, a marker of immune activation.
• Infected chimpanzees exhibited atypical diurnal cortisol patterns, with levels remaining high throughout the day.

Conclusions:

• Cortisol increase is directly linked to the cellular immune response in wild chimpanzees.
• Cortisol may mediate infectious disease pathogenicity by impacting the immune system.
• Wild primates face energetic stress when sick, demonstrating context-specific costs of immune defense.