SELECTION FOR REDUCED FEEDING IN LARVAE OF DROSOPHILA MELANOGASTER MIMICS THE DIETARY RESTRICTION EFFECT





P. F. FOLEY, L. S. LUCKINBILL

BIOLOGICAL SCIENCES,
WAYNE STATE UNIVERSITY,
DETROIT MI
48202




Experiments applying selection to create divergent populations for comparative study have usually left the nutritional intake of populations uncontrolled during the application of the breeding program. Caloric intake, however, exerts a strong influence on adult life span. The simple physiological restriction of food intake is well known to elicit a nongenetic increase in longevity resembling the genetically determined phenotype produced under selection. The question of whether reduced caloric intake extends longevity because it activates the pleiotropic genes that control life span, or merely evokes an artifactual response resembling genetic control, is a central unresolved issue in the study of aging. Though it has been successful in most respects as a model experimental organism for the study of aging, the fruit fly is unique in that nutrient restriction of adults does not elicit the extension of longevity widely documented in other experimental models. Drosophila melanogaster offers a novel opportunity, therefore, for the experimental exploration of this issue.


Here we compare the effects of selection for nutrient restriction of larvae with those of experiments in which selection was applied for longevity of adults. Divergent selection for nutrient use was applied by breeding for rapid and slow feeding larval D. melanogaster. Prior to pupating, fast-feeding larvae were found to engulf more food and synthesize more lipid, than larvae of slow feeding populations. Fast-feeding larvae eclosed to be short-lived as adult flies with high fecundity that peaked at an early age. Slow-feeding larvae had a reduced intake and synthesized less before pupating, but eclosed to become long-lived adults with a prolonged fecundity that was reduced in early life. Expression levels of Cu-ZnSOD, CATALASE and HSP70 were significantly elevated in long-lived populations. Genes favored under selection for reduced larval food intake exerted effects on adults that clearly mimicked the nongenetic physiological extension of life span seen other nutrient restricted model experimental organisms.


Strong parallel trends relate these results to those of preceding experiments. The effects on adults of selection for lower feeding rate in larvae resembled the effects on larvae of selection for life span in adults. Uptake, incorporation of food and synthesis onto lipid, the distribution of fecundity and life span of adult flies all varied in an identical manner to that of populations selected for long- and short-lived adult longevity. These results suggest nutrient limitation does affect life span via the same genetic elements and/or physiological control pathways that determine longevity.






Key words: Caloric restriction, longevity, Drosophila, selection







Problems or questions regarding this site should be directed to webmaster@americanaging.org