To investigate the relationship between food habits and digestive tract morphology, the lengths of gastrointestinal tracts of six species of rodents with different food habits were compared. The results showed that the strict herbivores, Microtus brandti, had the largest large intestine and ceacum, and the tracts of the other five granivorous/omnivorous species (Spermophilus daurica, Phodopus robovskii, Cricetulus barabensis, Cricetulus triton, Meriones unguiculatus) varied to different extents depending on the proportions of seed, vegetative and animal foods in their diets. Small intestine lengths did not reflect diet fiber content for these six rodent species and stomach lengths in granivorous/omnivorous rodents were not larger than herbivores. Our results suggest that the hind gut is more important for herbivorous than for granivorous/omnivorous rodents and could be a relative reliable indicator for food habits, however, small intestine is not a good indicator for food habits. This study also showed that there is no direct relationship between life history traits and gut morphology in these six rodent species, although more life history traits should be considered.
Metabolic rate, body temperature, and thermal conductance were determined in the greater long-tailed hamster (Cricetulus triton) at a temperature range of 5-36 °C. Oxygen consumption was measured by using a closed circuit respirometer. The thermal neutral zone was 39-34 °C. Within a temperature range of 5-31 °C hamsters could maintain a stable body temperature at a mean of 36.7±0.1 °C. Mean basal metabolic rate within thermal neutrality was 1.23±0.02 ml O2/g.h. Total thermal conductance was maintained within a temperature range of 5-15 °C (mean = 0.12±0.00 ml O2/g.h °C). The ecophysiological properties of the greater long-tailed hamster were: (1) a higher metabolic rate than predicted by the allometric scaling equation for eutherian mammals, but lower than that predicted for all rodents and slightly higher than predicted for cricetid rodents; (2) the body temperature was relatively low; (3) thermal conductance was relatively higher than predicted on the basis of body weight. All these characteristics are closely related to the species' life style (i.e. a burrowing, solitary, nocturnal species that feeds mainly on crop seeds and a small fraction of young crop shoots and insects). Greater long-tailed hamsters are primarily distributed in the northern Yangtse River area of China and cannot survive in extremely dr and alpine areas. We propose that the ecophysiological characteristics of the species might constrain its distribution and range extension into extreme deserts, high altitudes and cold areas.
A comparative study of resting metabolic rate was conducted for the temperature range 10-37 °C for four rodent species, northern three-toed jerboa (Dipus sagitta) (body mass, Mb 79.2±6.8 g, n = 25), midday gerbil (Meriones meridianus) (Mb = 45.0±8.1 g, n = 10), desert hamster (Phodopus roborovskii) (Mb = 15.4±2.9 g, n = 26, and striped hamster (Cricetulus barabensis) (Mb = 24.8±4.0 g, n = 7) in the Ordos desert in summer (July), 1997. The minimum resting metabolic rates were 1.14±0.25 ml O2/g.h for three-toed jerboa, 1.35±0.3 ml O2/g.h for midday gerbil, 2.98±0.65 ml O2/g.h for desert hamster, and 2.75±0.37 ml O2/g.h for striped hamster. The thermal neutral zones (TNZ) were wide in the three desert species that was 26~37 °C in jerboa, 26~35 °C in gerbil, and 24~34 °C in desert hamster, respectively. For the non-desert species, striped hamster, it was 26~30 °C. The results do not confirm the hypothesis that desert rodents generally have lower metabolic levels than non-desert species. The high metabolic rates of these four rodent species were interpreted to be influenced by the stable availability of food resources and low environmental temperature in the Ordos Plateau. our results partly support the hypothesis that the metabolism characteristics are determined by food resources and environment temperature for animals living in arid regions.
We examined the capacity for nonshivering thermogenesis in four rodent species residing in the Ordos Plateau of Inner Mongolia. Nonshivering thermogenesis (NST, maximum NST minus resting metabolic rate) was determined for northern three-toed jerboas (Dipus sagitta), midday gerbils (Meriones meridianus), desert hamsters (Phodopus roborovskii), and striped hamsters (Cricetulus barabensis) in spring (May), summer (July, and autumn (OCtober) captured in the Kubuqi desert in 1997. NST was induced by norepinephrine (NE) and measured by using the closed-circuit respirometer at 27 °C. Our results showed significant increases from summer to autumn in NST for the four species. NST capacities were 0.52±0.27 ml O2/g0.73.h (n = 7) in summer and 2.49±1.29 (n = 6) in autumn for jerboas, 1.61±0.74 (n = 6) in summer and 3.26±1.35 (n = 5) in autumn for gerbils, 3.62±0.75 (n = 5) in summer and 9.71±2.81 (n = 6) in autumn for desert hamsters, and 6.81±3.02 (n = 8) in summer and 11.23±2.77 (n = 8) in autumn for striped hamsters. These results suggest that small mammals living in the inland arid region on Ordos Plateau adapt to their extreme environment physiologically by adjusting their thermogenic capacities to cope with the dramatic seasonal temperature fluctuations.