TEMPERATURE REGULATION AND ADAPTATION * 

 TO GOLD GLIMATES 



J. Sanford Hart 



Studies conducted largely during the last 10 years have provided 

 us with a reasonably complete picture of the temperature regulation 

 of mammals in cold climates. It is clear that several types of ad- 

 justments to cold are theoretically possible, having been described 

 in previous reports byScholanderetal. (1950a) and Hart (1957). The 

 most economical is structural modification in which insulation of the 

 fur and tissues is increased to such an extent that very low ambient 

 temperatures can be tolerated without increased energy expenditure. 

 The most wasteful are metabolic modifications in which extremes of 

 low temperature that limit survival are extended only by increase in 

 metabolic rate. Behavioural adjustments (huddling, burrowing, etc.) 

 can modify costly metabolic requirements through avoidance of cold. 



The metabolic studies conducted on mammals have in general 

 been limited to short term tests which do not provide an integrated 

 picture of 24-hour energetics such as that provided for small birds. 

 Nevertheless, within the limitation of the methodology it has been 

 shown that quite distinct adaptive processes are in part dependent on 

 differences in body size and also in part on broad differences be- 

 tween aquatic and non-aquatic animals. Itwillbethe purpose of this 

 review to describe the temperature regulation and adaptation to cli- 

 mate found in free living mammals. The term "acclimatization" will 

 be used to describe individual physiological modification by climate 

 in nature while the term adaptation will refer to differences between 

 groups brought about through evolution. Other aspects of tempera- 

 ture regulation and acclimation to cold under laboratory conditions 

 will not be considered in this review since they have been treated 

 elsewhere (Garlson, 1954; Burton, 1955; Hart, 1957, 1958, and 1962; 

 and recent symposia, 1955, 1957, and 1960). 



♦Contribution from the Division of Applied Biology, NationalResearch Council, 

 Ottawa, Canada. Issued as N.R.C. No. 6580. 



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