Seasonal control of energy requirements for thermoregulation in the djungarian hamster (Phodopus sungorus), living in natural photoperiod |
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Authors: | Gerhard Heldmaier and Stephan Steinlechner |
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Institution: | (1) Zoologisches Institut, J. W. Goethe-Universität, D-6000 Frankfurt, Federal Republic of Germany |
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Abstract: | Summary Djungarian dwarf hamsters,Phodopus s. sungorus, were kept in natural photoperiodic conditions throughout the year, either inside at a constantT
a of 23°C or outside subjected to seasonally varyingT
a. Comparisons were made between hamsters from both conditions to evaluate the significance of seasonal changes in photoperiod and/orT
a as environmental cues for seasonal acclimatization inPhodopus. Basal metabolic rate was lowest in July (1.68 ml/g·h) and highest in January (2.06 ml/g·h inPhodopus living outside), combined with a decrease inT
1c from 26°C in July to 20°C in January. This was parallelled by seasonal changes in body weight (summer 42 g, winter 25g), fur colouration, fur depth and the occurrence of short daily torpor.AtT
a below thermoneutrality total energy requirements for thermoregulation in winter acclimatizedPhodopus were found 36% lower than summer values (e.g. at O°CT
a in summer 1,160 mW, in winter 760 mW), which were effected by a combined strategy of reducing body weight (19%) together with improvements of thermal insulation of the body surface (17%). All seasonal changes were similar inPhodopus living inside or outside, suggesting that seasonal changes in photoperiod and not seasonal changes inT
a is the overriding controller for the environmental cueing of seasonality in energy requirements for thermoregulation.This research was supported by the Deutsche Forschungsgemeinschaft (He 990) |
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