Androgen Elevation Accelerates Reproductive Senescence in Three-Spined Stickleback

Area of Science:

• Evolutionary biology
• Physiological ecology
• Animal behavior

Background:

• Reproductive costs influence life-history evolution, aging, and investment in current versus future reproduction.
• Androgens are implicated in regulating reproductive physiology and carotenoid-based sexual signaling.
• Androgens may divert resources to ornamentation, increasing oxidative stress and accelerating aging.

Purpose of the Study:

• To investigate the role of androgens (11-ketotestosterone) and antioxidants (vitamin E) in regulating reproductive investment, sexual signaling, and aging in male three-spined stickleback.
• To examine the trade-offs between current reproduction, future reproduction, and somatic maintenance.
• To explore the relationship between carotenoid-dependent coloration, life expectancy, and reproductive capacity.

Main Methods:

• A 2x2 experimental design was used to manipulate 11-ketotestosterone levels and vitamin E availability.
• Measurements included reproductive activity duration, reproductive effort (nest building, body composition), and nuptial coloration (redness, blue iris color).
• Correlations between coloration, life expectancy, and reproductive capacity were analyzed.

Main Results:

• Androgen elevation (11-ketotestosterone) significantly shortened the duration of reproductive activities.
• No direct evidence was found for increased reproductive effort (nest building, body composition) with androgen elevation.
• Carotenoid-dependent coloration was slightly reduced by 11-ketotestosterone and unaffected by vitamin E.
• Red coloration showed a quadratic relationship with life expectancy and reproductive capacity, suggesting potential overinvestment.
• Blue iris color was negatively correlated with survival, indicating physiological costs.

Conclusions:

• Results support the hypothesis that androgens regulate the balance between current and future reproduction, though mechanisms require further elucidation.
• The study highlights potential costs associated with exaggerated sexual ornamentation, impacting survival and aging.
• Quadratic relationships between sexual signal expression and fitness components have implications for understanding sexual selection and aging processes.