MAMMALIAN COLD ACCLIMATION 



While the temperature of the body skin was uniformly related 

 to the water temperature, temperatures of the appendages showed 

 striking fluctuations, suggesting independent control of heat loss, 

 which might be a basis for seasonal differences. The nature of the 

 fluctuations in temperature of the flippers was consistent with the 

 view that control of peripheral heat loss was affected by the pre- 

 sence of vascular heat exchangers, such as those described by Scho- 

 lander and Schevill (1955) for porpoises ( Lagenorhynchus acutus and 

 Tursiops truncatus). 



Comparison of Different Species 



Metabolic response to cold versus skin temperature . It is diffi- 

 cult to compare the metabolic responses of species which live in 

 such differentmelia as air and water. One basis is to make the com- 

 parisons relative to the actual body skin temperature of the species 

 in question. This has the merit of relating the response to some as- 

 pect of the animals' own perception system to which it must be re- 

 sponding rather than to some physical aspect of the environment. 

 The use of skin temperature is disadvantageous because it is highly 

 variable and is known only for a few species. Skin temperatures 

 measured over the mid part of the body on the flank or back of a 

 series of animals are correlated with oxygen consumption in Figure 

 12, as originally shown by Hart (19 6 2b). The sources of the data are 

 indicated in the legend. Comparisons of the same species relative to 

 air temperature are also shown. 



Clearly, the various species are distributed in a series with re- 

 spect to the sensitivity of the skin as a factor in the metabolic re- 

 sponse to cold. All the land mammals tested show increased heat 

 production at relatively high skin temperatures. Next in order is the 

 semi- aquatic muskrat, followed by the swine. The cooling of the 

 muskrat skin for the same metabolic response is not as great as that 

 for the harbor seal, especiallyduring the winter. The least sensitive 

 species was the harp seal, which showed no increase in metabolism 

 even in ice water. The range of responses indicates the very great 

 species differences that exist in toleration of peripheral cooling and 

 in temperature range of peripheral stimuli required to illicit that re- 

 sponse. It has also been shown for the harbor seal and for the leg 



221 



