DIRECT SELECTION ON LIFE-SPAN IN DROSOPHILA-MELANOGASTER

An important issue in the study of the evolution of aging in Drosophil a melanogaster is whether decreased early fecundity is inextricably co upled with increased life span in selection experiments on age at repr oduction. Here, this problem has been tackled using an experimental de sign in which selection is applied directly to longevity. Selection ap peared successful for short and long life, in females as well as males . Progeny production of females selected for long life was lower than for short-lived females throughout their whole life. No increase of la te-life reproduction in long-lived females occurred, as has been found in selection experiments on age at reproduction. This discrepancy is explained in terms of the inadequacy of the latter design to separate selection on life span from selection on late-life fecundity. Moreover , starvation resistance and fat content were lower for adults selected for short life. In general, the data support the negative-pleiotropy- disposable-soma theory of aging, and it is hypothesized that the pleio tropic allocation of resources to maintenance versus to reproduction a s implicated in the theory might involve lipid metabolism. It is argue d that further research on this suggestion is urgent and should certai nly comprise observations on male reproduction because these are for t he greater part still lacking. In conclusion, the longevity of D. mela nogaster can be genetically altered in a direct-selection design, and such an increase is accompanied by a decreased general reproduction an d thus early reproduction.