Growth and Senescence 

 5-2 Experimental Alteration of the Growth Rate 



5-2-1 INVERTEBRATES 



In many invertebrates, the specific age is easily altered, either 

 in response to temperature changes, to which it bears a simple 

 relation, or by retardation of growth through the restriction of 

 food. The total longevity of insects can be increased either by 

 underfeeding the larvae, or by keeping any or all of the stages, 

 from egg to imago, at low temperatures. The same applies to 

 ticks — starvation will increase the life-span of some species from 

 a few weeks to 2 years (Bishopp and Smith, 1938). Northrop 

 (Northrop, 1917; Loeb and Northrop, 1917) kept Drosophila 

 larvae for varying periods on a yeastless medium to delay 

 growth and induce stunting: by this means the total life-span 

 from hatching to death was increased. There is disagreement 

 whether delayed growth of larvae leads to an increase in the 

 life-span from eclosion. Northrop found no such increase in 

 imagines reared from retarded larvae. Intermittent starvation 

 of the imago of Drosophila shortens its life; retardation of 

 the larvae of Lymantria also fails to increase the life-span of 

 the imago, which cannot feed (Kopec, 1924, 1928). Alpatov 

 and Pearl (Alpatov and Pearl, 1929; Alpatov, 1930) found a 

 slight increase in imaginal life-span in Drosophila when the 

 larvae were retarded by development at 18°. This effect was 

 less evident in males, and appeared to be reversed in some 

 experiments: where the imagines were kept at 25-28° larvae 

 reared at 28° gave longer- lived flies than those reared at 18°. 

 The statistical significance of the differences was in any case 

 small. 



The life-span and final size of Daphnia (McArthur and 

 Baillie, 1926) and Moina (Ingle, 1933; Terao, 1932 etc.) vary 

 inversely with the temperature over a considerable range. Like 

 Drosophila, Daphnia can be markedly retarded either by cooling 

 or by underfeeding. A detailed study on the effect of retarda- 

 tion upon specific age and growth in Daphnia was carried out 

 by Ingle, Wood and Banta (1937). By diluting the medium, it 

 was shown that starvation of Daphnia for varying numbers of 

 instars resulted in an increase of life-span approximately equal 



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