Regulation by photoperiod of seasonal changes in body mass and reproductive function in gray mouse lemurs (Microcebus murinus): Differential responses by sex

Microcebus murinus exhibits highly seasonal biological rhythms to cope with extreme seasonality in availability of resources. To study the role of day length on seasonal changes in body mass and reproductive function, we expos ed male and female gray mouse lemurs to natural constant, or alternating li ght cycles for 2 years under constant environmental conditions. When expose d to either constant short (SD: 10 h light/day), long (LD: 14 h light/day), or intermediate (ID: 12 h light/day) daylength, males and females maintain ed a constant body mass with no spontaneous cyclic variation. We only obser ved typical seasonal body mass changes in subjects exposed to alternating p eriods of SD and LD, the weight gain being triggered by SD, whereas weight loss occurred under LD. Reproductive activity in females proceeded from an endogenous rhythm that was expressed under constant daylengths. In contrast changes in reproductive activity in males depended on daylength variation. In both sexes, SD and LD have direct inhibitory or stimulatory effects on reproductive activity. In females daylength regulates breeding season by sy nchronizing an endogenous sexual rhythm with the season whereas in males, t he perception of a critical photoperiod is used to determine the subsequent onset or arrest of their breeding season. These sexual differences in the effect of daylength could be related to sex-specific differences in reprodu ctive constraints.