Circadian rhythms of activity, metabolic rate and body temperature in desert hamsters (Phodopus roborovskii)
内蒙古草原小毛足鼠的活动性、代谢特征和体温的似昼夜节律

Most living beings change their behavior and physiology on a daily basis(24 h),with rhythmicity a fundamental property of living matter.Circadian rhythm is one of the important behavioral and physiological properties of wild animals.The desert hamster(Phodopus roborovskii) is a small rodent species which inhabits mainly desert and semi-arid environments in Inner Mongolia,China.Although field observations have shown that this species is mainly active at night,we know little about their biology and ecology,especially ecological physiology.In order to understand more about the behavioral and physiological adaptations of desert rodents,8 desert hamsters(4 males and 4 females,weighing 20.4 —27.5 g and aged between 11 and 13 months) were individually caged and kept under a temperature of(23±1)℃ and a photoperiod of(16L∶8D).Transmitters(ER-4000,Mini Mitter,USA) were implanted in the abdominal cavity of each hamster,and their body temperatures and activities were monitored for 24 h using a Vital View system.Their metabolic rates were also measured for 24 h using a TSE respirometry system(LabMaster,Germany).Our results showed that the average body temperature of the desert hamster is(37.27±0.39)℃ during the night and(36.11±0.18)℃ during the day.Their average metabolic rate is(4.65 ± 1.10)mLO2·g-1·h-1 and(3.09 ± 0.42) mLO2 ·g-1·h-1 during the night and day,respectively,and their average activity is(237±145) counts /0.1h during the night and(38±5) counts /0.1h during the day.Although ultradian activity rhythms were found over periods of 4,6,8,and 12 h,their amplitudes were much smaller than that of the 24h-circadian rhythm,which had a peak at(22.7±0.6) h.A similar pattern was observed for body temperature,which peaked at(23.1±0.5)h.Based on our analyses,body temperature,activity and metabolic rate all showed circadian rhythms and synchronization,with maxima during the night and minima during the day.These are typical properties of nocturnal animals,and support the idea that the desert hamster is a typical nocturnal rodent species.Behavioral observations in the field support this conclusion.Our results suggest that the desert hamster could be an ideal model for the study of the evolution and mechanisms of circadian rhythms inr wild animals.