Dietary Restriction and Trade-offs Between Survival and Reproduction

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Drosophila that have evolved enhanced longevity usually have reduced early reproduction. There are also negative correlations between reproduction and survival characters (e.g. starvation resistance) in D. melanogaster. Similarly, Drosophila and other organisms that have enhanced survival as a result of dietary restriction have reduced fertility. What is not clear is how nutrition and selection might interact with each other in the enhancement of survival, given that both are affected by this type of trade-off. The central questions for this project revolve around this interaction: (i) Can genetic trade-offs between survival and reproduction be surmounted by nutritional manipulation? (ii) Can selection change the effects of dietary restriction upon survival and reproduction? Two main experiments are planned. (1) Estimation of genetic correlations between early fecundity and starvation resistance (a factor that controls longevity) over four nutritional environments. This experiment would test the environmental dependence of genetic correlation. (2) Selection for increased starvation resistance under varying nutritional regimes: high or low nutrition before starvation and high or low nutrition after starvation but before egglaying. One of these selection regimes would favor the erosion of the normal dietary restriction (high then low nutrition), while one would favor it (low then high nutrition). The experiment would test the degree to which the dietary restriction response can be genetically changed by selection. Experiments (1) and (2) might reveal conditions under which trade-off between fecundity and starvation resistance is circumvented.