MAMMALIAN COLD ACCLIMATION 



correlation may be applicable to most fur bearers, but information 

 at present is inadequate. 



SUMMARY AND CONCLUSIONS 



The temperature regulation and adaptation of mammals to cold 

 climates follows different patterns in large and small mammals, and 

 in fur-bearing compared to bare- skinned or aquatic mammals. The 

 large arctic mammals with thickfur have a capability for withstand- 

 ing the severest climatic conditions without elevation of heat produc- 

 tion. This is accomplished by considerable cooling of the peripheral 

 areas and appendages as well as by great insulation of the fur. The 

 combined effect of these insulators provides a variable response 

 graded precisely to the temperature of the environment in a way not 

 yet fully understood. Climatic adaptation to arctic and tropical en- 

 vironments as well as acclimatization to summer and winter en- 

 vironments appears to be related to alteration in insulation of the fur 

 rather than to changes in body temperature or in metabolic rate. 

 However, infant animals of arctic species may be very sensitive to 

 temperature. 



In the mammals of small body weight, compensation for cold 

 through changes in insulation is not possible, and when protection is 

 inadequate, an elevation of heat production is necessary. Evidence 

 has been presented that small mammals such as mice and wild rats 

 show an increased cold resistance during the winter that is the re- 

 sult of the development of an increased metabolic capacity. It is 

 therefore apparent for the few species studied that cold exposure 

 and elevation of metabolism must have occurred during the winter 

 to account for the development of the observed seasonal acclimatiza- 

 tion. 



The only fur-bearing semi- aquatic mammal studied (muskrat) 

 showed no evidence ofseasonal change even though exposure to water 

 at 0° C during the winter seems inescapable. The surprising feature 

 of the study was the degree of body cooling observed during short 

 term exposure to cold water and the failure of fur insulation and 



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