Insulative Adaptation to Cold and Absence of Circadian Body Temperature Rhythm in Afghan Pikas : Ochotona rufescens rufescens

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概要

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• The pika inhabiting cold climate and high mountains is thought to be adapted to its environment. The autonomic characteristics of the high body temperature, high metabolism and poor heat loss ability such as poor panting, small ear pinnae and absence of thermal salivation as well as the behavioral characteristics, i.e. living in burrows under the ground or in the shelter among rocks and hoarding grasses for food to survive winter have been reported. However, insulative cold defense in pikas have not been studied and the pika's circadian activity rhythm remains controversial. In this study, the skin thickness and hairs length were histologically studied and the body temperature and locomotive activity were monitored in the freely moving pikas with a bio-telemetry system to clarify the pika's circadian rhythm. The hairs in the pikas were longer than the rats and more dense and 2 times longer on the dorsal region than the ventral region, though the skin was thinner. 20 mm of the hair length of the pikas was estimated to provide 3 Clo of insulative property. In contrast with the robust nocturnal rhythms in the rabbits and the rats, neither diurnal nor nocturnal body temperature rhythm was observed in the pikas, except for a slight increase at dawn and dusk consistent with the previous field observations. The pika is considered to be adaptive to cold not only ecologically and autonomically but also due to the insulative cold defense mechanisms. Though further investigation should be done, the absence of circadian body temperature rhythm in the pika is quite unique and attractive for the research field of circadian rhythm.

• 長崎大学熱帯医学研究所の論文
• 1997-03-24

長崎大学熱帯医学研究所 | 論文

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