Birth-season variation in Japanese macaques, Macaca fuscata

Area of Science:

• Primatology
• Animal Reproduction
• Ecology

Background:

• Japanese macaques (Macaca fuscata) exhibit a distinct annual reproductive cycle.
• The intrinsic regulation of this cycle is suggested by observations of minimal seasonal shifts after translocation within the northern hemisphere.

Purpose of the Study:

• To investigate the influence of latitude on the birth seasonality of Japanese macaques.
• To understand how environmental factors, particularly winter conditions, interact with latitude to shape reproductive timing.

Main Methods:

• Observational study of Japanese macaque troops translocated to different latitudes.
• Analysis of birth seasonality data in relation to troop locality and latitudinal zones.
• Comparison of birth timing patterns across different latitudinal gradients.

Main Results:

• Translocation to the southern hemisphere caused a significant 6-month shift in birth seasonality.
• Within a specific latitudinal zone (Toimisaki to Kinkazan), earlier birth dates were observed at higher latitudes.
• This latitudinal relationship was not consistent outside this specific zone, suggesting complex environmental interactions.

Conclusions:

• While intrinsically regulated, Japanese macaque reproduction is sensitive to latitudinal cues and associated environmental conditions.
• Optimal birth timing appears linked to balancing infant development with seasonal resource availability, particularly winter food conditions.
• The adaptive significance of birth seasonality varies with latitude due to differing winter severity and duration.