Photoperiod-induced changes in energy balance in gray mouse lemurs

To cope with the 6-month dry winter occurring in its natural habitat, the gray mouse lemur (Microcebus murinus), a Malagasy prosimian primate, exhibits a pre-wintering fattening phase that has been previously demonstrated to be dependent on the photoperiod. To assess early changes in energy balance following a photoperiodic shift, food intake (FI), resting metabolic rate (RMR), plasma triglycerides, plasma thyroxine and urinary excretion of cortisol were measured in 12 males and 12 females for 8 weeks following a shift from short (SP: 10 h light/day) to long (LP: 14 h light/day) photoperiod or from LP to SP. Shift from LP to SP led to a high, linear body mass (BM) increase in both sexes, concomitant to an increase in plasma triglycerides and a decrease in plasma thyroxine, while no change in RMR occurred. FI significantly increased from 30 to 40 kcal/day as early as the first week following SP exposure but spontaneously decreased after 4 weeks, reaching minimal values (10 kcal/day) after 14 weeks of SP exposure. Shift from SP to LP led to a decrease in BM and an increase in FI, but both were slow and different between males and females. No change in RMR was observed except a significant increase in males during the first week of LP exposure. However, plasma thyroxine levels and cortisol excretion similarly increased in both sexes following LP exposure. These results suggest that autumnal fattening mainly proceed from changes in FI and in thyroxine secretion triggered by exposure to SP. In contrast, BM loss following LP exposure would be related to seasonal sexual activation rather than to a direct control by photoperiod.