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The metabolic switch hypothesis refers to an ability to adjust metabolic rate. It plays a key role in animals adapted to periods of food shortage, enabling them to "switch down" their resting metabolic rate and to survive and maintain their weight indefinitely on limited rations. The present study investigates the energy strategies of a small mammal in response to food shortages as a function of food restriction, metabolic rate and ambient temperature. We subjected tree shrews (Tupaia belangeri) to food restriction and measured body mass, survival rate, resting metabolic rate, non-shivering thermogenesis and cytochrome c oxidase activity of brown adipose tissue. Cold-exposed animals restricted to 80% of ad libitum food intake had significantly increased resting metabolic rate and non-shivering thermogenesis and decreased body mass and survival rates compared with those kept as control group on the same ood restriction level. Animals classified as having a high resting metabolic rate consumed 30.69% more food than those classified as having a low resting metabolic rate, but showed no differences in body mass or survival when restricted to 80% of ad libitum food intake. These results indicate that tree shrews, known for their relatively high metabolic rates, are sensitive to periods of food restriction, which supports the metabolic switch hypothesis. Our findings are also consistent with the prediction that small mammals with food hoarding behaviors, like tree shrews, may have a lower tolerance for food shortages than non-hoarding species. [ABSTRACT FROM AUTHOR]

Phenotypic plasticity is the capacity for individuals to modify their phenotype in response to environmental changes. For example, variation in external and cranial characters have been documented in some small mammals and can result in controversy over classification, which has been the case for tree shrews for decades. However, there are few reports about external and cranial character variation in tree shrews (Tupaia belangeri). Here, such character variants of tree shrews were documented for 11 different sampling sites (Hainan, Daxin, Leye, Xingyi, Hekou, Kunming, Xichang, Dali, Pianma, Tengchong, Mengla) and for laboratory samples. The results showed that external and cranial characters of tree shrews significantly differed among regions, Hainan and Daxin populations were significantly larger than those of other populations, and Leye, Xingyi, Kunming and Xichang populations were smaller. The variation may be related to the habitat of tree shrews and our data may initiate new interest in morphological variants in small mammals. The presented detailed examination of the morphometric characters in tree shrews, and the exposed significant morphological differences among tree shrews, are expected to help in confirming their classification status. [ABSTRACT FROM AUTHOR]

Small mammals are usually adapted to cope with changes in food quality and availability. In order to investigate the adaptive strategy of small rodents responding to varying dietary fiber content, in the present study, Apodemus chevrieri individuals were acclimated to a high-fiber diet for four weeks and then a relatively low-fiber diet for another four weeks. The results show that body mass was relatively stable over the course of acclimation, but dry matter intake, gross energy intake and the mass of the digestive tract increased significantly and digestibility decreased significantly in high-fiber diet mice, while the digestible energy intake was similar for both high-fiber and low-fiber diet mice except for the first week. High-fiber/low-fiber diet mice showed only a significant lower basal metabolic rate and nonshivering thermogenesis compared to low-fiber diet mice on day R1. The high-fiber diet induced a decrease in serum leptin levels and brown adipose tissue mass associated with a reduction in the cytochrome c oxidase activity and uncoupling protein 1 content of brown adipose tissue. Body mass, thermogenic capacity, energy intake, serum leptin levels and digestive tract morphology returned to the control levels after 4 weeks of refeeding low-fiber diet. Further, serum leptin levels were positively related to body fat mass and negatively related to food intake. These data indicated that body mass, energy intake, serum leptin levels and organ morphological plasticity were the main strategies by which A. chevrieri copes with variations in dietary fiber content. [ABSTRACT FROM AUTHOR]

Physiological adjusimenis are important strategics for small mammals in response to variation in food availability. To determine the physiological mechanisms affected by food restriction and releeding, tree shrews were restricted to 85% of initial food intake for 4 weeks and refed ad libitum for another 4 weeks. Changes in food intake, body mass, thennogenesis. body composition, mitochondrial cytochrome c oxidase activity, uncoupling protein-1 content in brown adipose tissue and scrum lcpiin levels were measured. The results showed that body mass, body fat mass and serum leptin levels significantly decreased in food restricted tree shrews, and increased when the restriction ended, showing a short "compensatory growth" rather than over-weight or obesity compared with ad libitum controls. Resting metabolic rate, non-shivering thennogenesis, brown adipose tissue mass (mg). and uncoupling protein-1 content decreased significantly in response to food restriction, and returned to the control levels after the animals were refed ail libitum, while the brown adipose tissue mass (%) and cytochrome c oxidase activity remained stable during food restriction and refecding. Food intake increased shortly after releeding, which perhaps contributed to (he rapid regaining of body mass. These results suggest that Tupaia bclangeri can adjust the status of its physiology intcgratively to cope with the lack of food by means of decreasing body mass, thennogenesis and scrum leptin levels. Leptin may act as a starvation signal to predominantly mediate the reduction in body mass and energy expenditure. [ABSTRACT FROM AUTHOR]

Environmental cues, including photoperiod and temperature, play important roles in the adjusting of physiology and behavior in small mammals. In order to determine the contributions of short pho-toperiod and cold temperatures to seasonal changes in body mass and thermogenesis in Eothenomys miletus, body mass as well as several physiological, hormonal, and biochemical markers (indicative of thermogenic capacity) were examined in seasonally-acclimatized and lab-acclimated animals. Hereby we test our hypothesis that E. miletus can adjust body mass and thermogenesis capacity to survival in winter or short photoperiod and cold temperatures. The results showed that E. miletus adapted to winter by decreasing body mass, and this change was mimicked by exposing animals to cold tem-peratures and short photoperiod in the lab. E. miletus increased energy intake and thermogenesis and decreased body fat mass and serum leptin levels in winter or under cold temperatures, but not un-der short photoperiod. Protein contents and uncoupling protein 1 contents of brown adipose tissue increased significantly in winter or at cold temperatures, but not under short photoperiod. Together, these data suggest that the observed physiological regulations from the organismal, hormonal levels to the cellular level of E. miletus are critically important and allow E. miletus to successfully overcome the physiological challenges of a cold environment in winter by increasing thermogenic capacity, en-ergy intake and decreasing body mass and body fat mass. It seems that E. miletus is more sensitive to cold temperatures and leptin may play a potential role in seasonal regulation of body mass and thermogenesis. [ABSTRACT FROM AUTHOR]

To investigate the effect of fasting and re-feeding on energy metabolism and thermogenesis in the tree shrew (Tupaia belangen), the changes in body mass and body fat mass, resting metabolic rate (RMR), non-shivering thermogenesis (NST), body composition, mitochondrial cytochrome c oxidase (COX) activity in liver and brown adipose tissue (BAT), uncoupling protein-1 (UCP1) content of BAT, serum Ieptin level and post-fasting food intake were monitored and measured. The results showed that fasting induced a significant reduction in body mass and body fat mass. Body mass was restored to the control level in re-feeding tree shrew except for the body fat. RMR and NST decreased significantly in response to fasting, and returned to the control level after re-feeding. Fasting induced significant reduction in total, but not specific, COX activity (nmol 02/min/total tissue) in liver and BAT, and UCP1 content in BAT, which was reversed after re-feeding 48 h. Fasting of 12 h induced a rapid reduction in serum leptin content. There were no post-fasting compensatory increases in food intake. Interestingly, the tree shrew did not recover adipose tissue mass, nor serum leptin levels, upon re-feeding. These results suggest that T. belangen can adjust the status of its physiology integratively to cope with the lack of food by means of decreasing body mass, adaptive thermogenesis and serum leptin levels, and serum leptin level acted as a starvation signal to mediate predominantly the reduction in body mass and energy expenditure. [ABSTRACT FROM AUTHOR]

Environmental cues play important roles in the regulation of an animal's physiology and behavior. In the present study, we examined the effects of short photoperiod on body weight as well as on several physiological, hormonal, and biochemical measures indicative of thermogenic capacity to test our hypothesis that short photoperiod stimulates increases in thermogenesis without cold stress in Apodemus chevrieri. A. chevrieri were randomly assigned to either a long or short photoperiod for 4 weeks at constant temperature. The short photoperiod group of A. chevrieri showed increases in resting metabolic rate and nonshivering thermogenesis during the 4-week photoperiod acclimation. At the end, A. chevrieri at short photoperiod had lower body weights, higher levels of mitochondrial protein content and cytochrome C oxidase activity in liver and brown adipose tissues, and had higher levels of mitochondrial uncoupling protein-1 contents in brown adipose tissues. No difference in serum leptin levels were found between short and long photoperiod groups, but serum leptin levels were positively correlated with body mass and body fat mass, and negatively correlated with energy intake and uncoupling protein-1 content in brown adipose tissues, respectively. All results suggest that the short photoperiod may induce an increased thermogenesis capacity in A. chevrieri and that leptin is potentially involved in the photoperiod induced body mass regulation and thermogenesis in A. chevrieri. [ABSTRACT FROM AUTHOR]

Seasonal changes in an animal's morphology, physiology, and behavior are considered to be an adaptive strategy for survival and reproductive success. We hypothesize that Apodemus chevrieri will change their thermogenesis seasonally and serum leptin will change with body mass or body fat mass. Seasonal variations in body mass (BM), basal metabolic rate (BMR), nonshivering thermogenesis (NST), digestive tract morphology, serum leptin and uncoupling protein 1 (UCP1) were measured in wild-trapped A. chevrieri in Hengduan mountain region. The results showed that the body weight of A. chevrieri was lowest in winter and highest in summer. Decreased BM in the winter was accompanied by increased energy intake and enhanced NST and UCP1 as well as by decreased body fat mass, adjusted digestive tract morphology and reduced levels of circulating leptin. Further, serum leptin were positively correlated with body weight and body fat mass, and negatively correlated with energy intake and UCP1 contents. These data suggest that wild A. chevrieri do not depend on a decrease in BM, but instead increase their thermogenic capacity to cope with cold stress. Leptin may be involved in the seasonal regulation in energy balance and thermogenesis in field A. chevrieri. [ABSTRACT FROM AUTHOR]