242 Comparative Animal Physiology 



"basal" rate of oxygen consumption for the goldfish, Carassius, increases up to 

 a temperature of 35° C, but during activity the maximum metabolic llvel is 

 limited to approximately 30° C. The "maximum steady state," the condition of 

 normal activity, at various temperatures, is definitely related to given rates of 

 oxygen uptake, the higher the temperature maintained the greater the oxygen 

 consumption (Fig. 53). At reduced tensions the oxygen consumption rapidly 

 falls off, being affected at a higher oxygen tension for the higher metabolic 

 rate, indicating the inability of the fish to maintain the specific activity at the 

 designated temperature. One should not lose sight of the fact, moreover, that 

 the solubihty of oxygen is much reduced at the higher temperatures, although 

 activity is increased. High temperature tolerance is directly associated with 

 organic composition, particularly that of the unsaturated fatty acids, and this 

 is frequently reflected in the gas exchange and R.Q. The effects of age and 

 size on temperature adjustment are important as seen in recent evidence on 

 sand crabs, click beetles, beach fleas, and killifish, which clearly indicate that 

 smaller animals in a species respond to temperature changes more markedly 

 than do larger onesi"-'' -^"o (Fig. 54). 



Metabolic adaptations to temperature differences have been noted in rela- 

 tion to species adjustment in Drosophila (p. 235) and to seasonal acclimatiza- 

 tion among crustaceans and fish (p. 240). Likewise adaptations to tempera- 

 ture variations associated with geographic distribution of Crustacea may be 

 demonstrated, as in the comparison of oxygen consumption by prawns from 

 Swedish and from English waters. When measured at the temperatures of 

 their natural environments (5 and 15° C.) Swedish crayfish consume less 

 oxygen than their English relatives. However, if measured at the same 

 temperature (10° C), the metabolic rate of the northern forms may exceed 

 by more than twice that of the southern specimens.^ ^-' ^^'^ As locomotion, 

 breathing movements, and heart rates of the southern species are only slightly 

 increased over those of the northern species (the animals being to this extent 

 somewhat acclimatized to their warmer environment), the higher metabolic 

 rate of the English crayfish may be explained as due to their greater "non- 

 activity" metabolism (see Chapter 10). 



When measurements were made at the same temperature— 16° C— river 

 lampreys from a 3° C. environment consumed about 50 per cent more oxygen 

 than those from 16° C. waters.-^^^ The same sort of acclimatization has been 

 observed in Drosophila. On the other hand, when both are measured 

 at 25° C, Amhlystoma raised at 20° C. have a higher rate of oxygen consump- 

 tion during early development than those reared at 15° C. 



Benedict-^ has generalized the situation by stating that, when the tempera- 

 ture of the environment is lowered to 10° C, the metabolic activity of warm- 

 blooded animals will always exceed that of cold-blooded animals at that 

 temperature, and, conversely, when the temperature is elevated to the region 

 of 37° C, the metabolic heat production of the poikilotherms will never 

 exceed 34 per cent and will average 12.5 per cent of that of the homoiotherms 

 at this temperature. 



Diurnal and seasonal rhythms in the temperature-ox>'gen consumption 

 relationshi]) are important in many organisms— much of which has to do with 

 daily routine on the one hand and with seasonal adjustment on the other. An 

 apparently endogenous diurnal variation in oxygen consumption, possibly 



