POIKILOTHERMIC ADAPTATIONS 



metabolism and behavior with changing body temperature, whereas 

 the acclimation of homeotherms tends toward maintenance of con- 

 stant body temperature. Some poikilotherms show no compensations, 

 but their body processes remain slow (as in hibernation) at low tem- 

 peratures. 



No consistent pattern is yet evident for biochemical changes. 

 According to in vitro measurements, some enzymes appear to com- 

 pensate; many do not. Glycolysis may be most affected in fish. The 

 meaning of lipid changes is not clear , although lower melting points 

 in the cold are found in fish as well as in peripheral fat of mammals. 



The integrated metabolic system of intact animals shows more 

 consistent compensation than isolated enzymes. Undoubtedly hor- 

 mones are important in acclimation, as shown by the effects of 

 photoperiod. However, there is evidence for direct effects of tem- 

 perature, possibly through some sort of enzyme induction. Marked 

 differences occur in the response of different organs and tissues to 

 temperature. 



Behavioral compensations reflect a heirarchy of differences in 

 nervous adaptations with complex conditioned responses being most 

 sensitive and pe;ripheral nerve conduction least. These changes in 

 sensitivity of nervous systems to cold might be related to alterations 

 in membrane lipids. 



Changes in resistance to extreme temperature stress are clear- 

 ly indicated by decline in temperatures of both heat and cold death 

 with reduced acclimation temperature. Mechanisms of changes in 

 resistance to temperature extremes are unknown as are the rela- 

 tions between compensation (capacity) acclimation and resistance 

 acclimation. 



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