Photorefractoriness and Recovery of Photosensitivity in a Seasonal Nonhuman Primate ( Microcebus murinus )

Primates show a range of reproductive seasonality patterns, from year-round to strictly seasonal breeding. Seasonality depends on several factors, such as food availability, which dictates patterns of optimal and nonoptimal periods for reproduction, and is usually triggered by photoperiod in high latitudes. Photorefractoriness is a state of unresponsiveness to the prevailing photoperiod, characterized by spontaneous gonadal regression at the end of the breeding season and spontaneous anticipated gonadal development at the end of the resting season, preventing reproduction from occurring at the wrong time. Despite its importance in understanding primate reproductive physiology and adaptation to seasonal changes, photorefractoriness has been described in only one highly seasonal primate species so far: the gray mouse lemur ( Microcebus murinus ). In this study, we assessed the time required for male and female mouse lemurs to recover photosensitivity to short-day (SD) and long-day (LD) photoperiods. To test the recovery of photosensitivity to SD, we transferred 25 females and 40 males to SD after 4, 6, 8, 10, or 22 weeks in LD. To test the recovery of photosensitivity to LD, we applied the opposite protocol with 4, 6, 8, 10, or 14 weeks in SD. We monitored body mass, testosterone plasma levels and estrus every 2 weeks. We found that refractoriness in body mass lasted 10 weeks in both sexes, whereas females regained reproductive function in 4 weeks and males did so in 8 weeks. These results highlight that body mass and reproductive functions demonstrate distinct and sex-specific responses to photoperiod in mouse lemurs.