Reproduction in the vervet monkey (Cercopithecus aethiops): I. Testicular volume, testosterone, and seasonality

Area of Science:

• Primate reproductive biology
• Mammalian endocrinology
• Behavioral ecology

Background:

• Vervet monkeys exhibit seasonal birth peaks in both wild and captive populations.
• The role of male reproductive physiology in these seasonal birth patterns remains unclear.

Purpose of the Study:

• To investigate the potential contribution of male vervets to seasonal birth peaks.
• To assess seasonal variations in testicular volume and testosterone levels in adult male vervets.

Main Methods:

• Monthly measurements of testicular volume and peripheral testosterone concentrations over 14 months in nine adult male vervets.
• Quarterly testicular biopsies to assess spermatogenesis and sperm presence.
• Correlation analysis between reproductive parameters, breeding status, and time of year.

Main Results:

• Testicular volume showed a modest 15% increase during the June-September breeding season compared to other periods.
• Testosterone levels increased throughout the study but did not correlate with testicular volume.
• Spermatogenesis and spermatozoa were present year-round, irrespective of breeding status or testicular volume.
• No significant correlation was found between testicular volume and breeding status or biopsy findings.

Conclusions:

• Seasonal fluctuations in male vervet testicular volume and testosterone are small and unlikely to drive observed birth peaks.
• Year-round spermatogenesis suggests males are capable of breeding throughout the year.
• A significant physiological contribution by males to natural birth peaks is not evident from this study.