2l6 GROWTH PRINCIPLES AND THEORY 2 



(/)) Growth and temperature 



Owing to the possibility of measurement and physicochemical interpretation, 

 effects of temperature are of particular significance for the theory of growth. 



According to the classical Bergmann rule (1847), animals of the same species 

 are, in general, larger in cold climates than in warm ones. Bergmann interpreted 

 the temperature rule in terms of the heat economy in homeothermic animals. Loss 

 of heat is proportional to body surface; the latter decreases in its ratio to body 

 weight with increasing size; therefore less heat per unit weight has to be produced 

 in a larger animal in order to keep body temperature constant. Thus increase in 

 body size saves energy and is adaptive in cold climate. Conversely, smaller body 

 size and relatively increased surface facilitate heat output in warmer surroundings. 

 In this way, Bergmann's geographical rule for body size is a precursor of Rubner's 

 physiological rule for metabolism (p. 181). 



It is found, however, that Bergmann's rule also applies in poikilothermic 

 animals where Bergmann's (and Rubner's) explanation evidently is not applicable. 

 Two cases of the relation between temperature and body size can be distinguished. 

 The first is genotypical, that is hereditary differences in body size which presum- 

 ably can be explained in the way proposed by Bergmann, i.e. selective advantage 

 of larger body size in cold, and of smaller size in warm climates. The second case 

 is phenotypical variations, that is direct influence of temperature on growth. As a 

 crude rule of thumb it may be stated that the first especially applies to differences 

 in body size as found in geographical races of warm-blooded animals; the second, 

 to many observations and experiments with invertebrates and poikilothermic 

 vertebrates. This, however, is by no means a clear-cut distinction; geographical 

 races with varying body size are also found in poikilothermic animals, and 

 conversely direct effects of temperature on growth in mammals. Only the second 

 case will be discussed here. 



In the sense of the theory presented, the following inferences can be drawn. 

 The catabolic processes can be considered as being, in the last resort, of chemical 

 nature; therefore they will have a high temperature coefficient as characteristic 

 of chemical reactions according to Van 't Hoff's rule. The anabolic processes, on 

 the other hand, lastly depend on the import of materials regulated by factors of 

 permeation, diffusion, etc., i.e. physical processes likely to have a low temperature 

 coeflftcient. When, with increasing temperature, the catabolic constant x of the 

 growth equation is strongly increased, but the anabolic constant y] undergoes 

 little change, two consequences follow: i. Growth rate will increase, and 2. final 

 size will decrease. That is, with increased temperature the organism will grow 

 faster toward a smaller final size. This is, as a general rule, found in observation. 



The complexity of the relationships between tissue respiration, body size, temperature, 

 fasting (Locker, i958d), pharmacological agents such as dinitrocresol (Locker and Hofer, 

 1958; Locker, 1958b), etc., have already been mentioned (p. 187). 



The above conclusions correspond, as a rule, with experience in unicellular organisms. Cell 

 size in general decreases with increasing temperature (Table 12; similar results with 

 Frontonia, Stylonychia: PopofT; Paramecium: Rautmann; Foraminifera: Rhumbler; survey of 

 literature in Belehradek, 1 935 ; Margalef, 1 954) . An exception is the yeast, Torulopsis kefir 

 (Christophersen and Precht, 1954; cf. p. 205). 



In invertebrates and fisli, the above rules are confirmed by many examples in animal 



