Different polymorphic elements of the enzyme glucose-6-phosphate dehydrogenase (G6PD) are favoured under selection for long versus short life span. Replicate independently selected populations of short-lived individuals exhibit a more rapidly migrating and less actively staining allozyme, while long-lived populations have a slower migrating and more active allozyme. These correspond to the common ZwA and ZwB variants of the G6PD locus Zw. In vitro measurements show G6PD activity varies with allozymes and life span. Long-lived males have 64 per cent greater activity in G6PD, while females of long-lived strains are 108 per cent higher than those of short-lived strains. Previous studies of these strains have repeatedly demonstrated additivity of life span in F1 crosses. Activity of G6PD in reciprocal F1 populations is additive and intermediate between parents.
Models of the evolution of life span predict, and gerontological studies show, a relation between nutrient use and life span. This study examines the role and comparative use of nutrients in long- and short-lived populations of D. melanogaster selectively bred for age-at-reproduction, without respect to metabolism or feeding rate. We test the hypotheses that selection for life span has favored the restriction of nutrient use and that the observed effect of low population density during development is a consequence of modifying nutrient use. The use of nutrients was measured here by the uptake of radiolabeled glucose, its incorporation into lipid and protein, and by the in vivo metabolic flux through the pentose shunt. Measurements show that uptake, incorporation, and flux are severely limited in long-lived stocks, compared to short-lived populations of the same stage and stage of development. Raising long-lived stocks at low population numbers relieves the restriction on metabolism in larvae, increasing incorporation and flux, and causes adult life span to decline. Larvae of long-lived populations appear to feed less actively, suggesting that the reduction in use of nutrients could simply be from reduced intake. Changes in total soluble protein correspond with measurements of uptake, incorporation, and flux. Soluble protein is substantially less in long-lived stocks, before pupation, but catches up in early adulthood to that in the short-lived populations. Despite different nutrient use by larval populations, only slight differences are found in development rate. They are insufficient to account for the differences observed in longevity.
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