MAMMALIAN COLD ACCLIMATION 

 DISCUSSION 



MORRISON: I have some data on related species living in 

 the same environment. These show differing thermal sensitivi- 

 ties that can be rather nicely correlated with their habits. I hope 

 this will be of interest because it represents work done with 

 Dr. F. A. Ryser in this laboratory some years ago. 



These are simply measurements of the body temperature 

 against the ambient temperature. Figure 14 compares the two 

 common voles taken from the nearby Chena River in February 

 and March. Clethrionom ys has excellent regulation. Microtus, 

 on the other hand, falls off badly at low ambient temperatures 

 both in regard to the summer temperature and the higher winter 

 temperature. This correlates with their habits since Microtus 

 stays strictly inside its burrow system when it is cold, whereas 

 Clethrionomys does come out and move around. 



Figure 16 compares the two lemmings from the far north. 

 Dicrostonyx regulates well but Lemmus is not so effective. 

 Dicrostonyx is seen above the snow when it is very cold whereas 

 L emmus carefully restricts himself to his subnivean micro- 

 climate. Incidentally, Dr. Hart showed a slide from Dr. Scholander 

 (Hart, Fig. 2) on insulation values in various northern mammals. 

 There the lemmings were grouped, but the two highest values 

 represented Dicrostonyx while the four lower points were for 

 Lemmus, which difference correlates with the physiology and 

 behavior. 



HART : How long were the exposures of the Microtus ? 



MORRISON: These were caged animals living at these low 

 temperatures, so there were a number of hours of exposure, days 

 in some cases. 



HART: Continuous exposure? 



MORRISON: Yes. 



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