The Biology of Senescence 



greater homozygosis for adverse genes, the effect should be 

 reversed in those forms where the female is heterogametic — 

 notably lepidoptera and birds. From the studies of Landauer 

 and Landauer on fowls (1931) and of Rau and Rau (1914) on 

 saturnid moths, they could find no evidence of such a reversal. 

 Adequate life-table studies are still very scarce in these groups. 

 In crosses, the difference in vigour between homogametic and 

 heterogametic sexes may certainly be so great that only the 

 homogametic reaches maturity — thus Federley (1929) found 

 that in certain interspecific crosses in hawk moths, only the 

 males survived pupation, though in reciprocal crosses both 

 sexes survived. Beside these studies, that of Pearl and Miner 

 (1936) upon Acrobasis caryae, which is one of the few actuarially- 

 constructed lepidopteran life-tables which have been published, 

 and an extensive study by Woodruffe (1951) on the survival of 

 the moth Hofmanophila pseudospretella under different environ- 

 mental conditions both show a significantly higher female life- 

 span. Alpatov and Gordeenko (1932) working on Bombyx mori, 

 found no difference in longevity between unmated males and 

 females, but a significantly longer male life in mated moths. Re- 

 examining the results of Rau and Rau (1914) they concluded 

 that in both Samia cecropia and Calosamia promethea the mated 

 female had a shorter life-span than the male. This difference, 

 however, might be due at least in part to the exhaustion of 

 reserves by more frequent egg-laying in mated females. The 

 life-span of the female Aglia tau is said to be the shorter 

 (Metchnikoff, 1907). 



Rey (1936) working on the non-feeding imago of the moth 

 Galleria mellonella, found that the males lived up' to twice as long 

 as the females, the difference being unaffected by humidity but 

 exaggerated at low temperatures. He assumes this to be 'the 

 rule for lepidoptera'. 



In poultry, it seems to be established that the female is the 

 more viable and has the longer reproductive life (Pease, 1947) 

 and observations such as those of Mcllhenny on wild ducks 

 (1940), which indicate an increase in the proportion of males 

 with increasing age, are probably the result of differential risks. 

 Longer life-span in males is also found in some other birds in 

 the wild (Lack, 1954). In cyprinodont fishes, some of which have 



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