Plasticity in the physiological energetics of Mongolian gerbils is associated with diet quality

Small mammals usually show physiological and behavioral adaptations to cope with seasonal changes in food quality and availability. To examine the adaptive strategy of small rodents responding to varying dietary quality, we acclimated Mongolian gerbils (Meriones unguiculatus) to a high-fiber diet (HF: 35.5% neutral detergent fiber [NDF] and 21.4% acid detergent fiber [ADF]) for 4 wk and then a relatively low-fiber diet (LF: standard rat chow, 12.8% NDF and 4.8% ADF) for another 4 wk. Body mass was stable over the course of acclimation, but food intake and the size and mass of the digestive tract increased significantly in HF gerbils. The HF diet induced a decrease in basal metabolic rate and nonshivering thermogenesis associated with a reduction in the uncoupling protein 1 content of brown adipose tissue. After 4 wk of subsequent feeding on the LF diet, body mass, energy intake, digestive tract morphology, and thermogenic capacity recovered to the baseline. Serum leptin level decreased in HF gerbils and increased in the gerbils then fed with the LF diet. Further, the change in serum leptin level was positively related to body fat mass and negatively related to food intake, suggesting that the decreased leptin level associated with lower body fat content might be a signal that an animal was in negative energy balance. Finally, our data indicated that energy intake, body composition, and organ morphological plasticity are the main strategies by which gerbils cope with variations in food quality. Change in serum leptin level is related to change in food intake in Mongolian gerbils.