Discussion 267 



Rockstein: Do they lay eggs? 



Maynard Smith : Yes. The more protein you give them as larvae, 

 the higher the rate of egg-laying when they are adults. We therefore 

 suspected that the ones which had a lot of protein might not live as 

 long as the others, but there is no overall effect of any great magni- 

 tude. If there is an effect it is of the order of 10 or 20 per cent — not 

 more than that. 



Kershaw: There is an analogous situation in parasitism. The 

 ability of the tsetses to act as vectors of sleeping sickness is largely 

 determined by the temperatures at which the pupae are maintained 

 before the adults come out. What effect that has on the longevity 

 of the adult is not known, but it will be a sort of parallel viability, or 

 parallel parameter that we put against longevity. 



It is the middle-aged insect which is the important survivor for 

 parasites, because the ones which die young do not hve long enough 

 to transfer the parasite. Secondly, a very complex pattern of 

 mortality is evident in the development of a parasite in different 

 selected organs of an insect. A third point is the ability of the insect 

 to support the parasite, so that those at the tag end of their life 

 cannot act as vectors. That has an obvious application in the field 

 but what this means biologically one does not know. Unfortunately 

 there are no means at the moment of quantitatively assessing the 

 capacity of insects to support some parasites. 



Wigglesworth : Could you describe the sexual difference in the 

 effect of protein feeding by saying, rather as Prof. Kershaw is im- 

 plying, that the adult male is not protein- starved, but that the adult 

 female is starved of protein by its reproductive activities — therefore 

 in the absence of the extra protein feeding it succumbs early? 



Rockstein: Yes, that inference would be very appropriate. 



Sacher: I found a survivorship curve for male Drosophila almost 

 identical with what you found for the male housefly. Prof. Rockstein. 

 Unfortunately I did not get data for female Drosophila. In regard to 

 your remarks about the complexity of the survivorship curve for the 

 female (and I think we should say for the male too), perhaps we 

 should recall the controversy between Crozier and Pearl (Pearl, 

 R., White, P., and Miner, J. R. (1929). Proc. nat. Acad. Sci. (Wash.) 

 15, 425). Pearl had studied the resistance of Drosophila to alcohol 

 as a function of age and he got a curve which he graduated smoothly. 

 Crozier (Crozier, W. J., Pincus, G., and Zahl, P. A. (1936). J. gen. 

 Physiol., 19, 523) objected that such smoothing was not proper and 

 he did a far more extensive experiment. He established that the 

 resistance of Drosophila to alcohol as a function of age went through 

 many stages and was an exceedingly complex curve. This comes 



