Evolutionary Optimality Applied to Drosophila Experiments: Hypothesis of Constrained Reproductive Efficiency

Abstract

The general purpose of the paper is to test evolutionary optimality theories with experimental data on reproduction, energy consumption, and longevity in a particular Drosophila genotype. We describe the resource allocation in Drosophila females in terms of the oxygen consumption rates devoted to reproduction and to maintenance. The maximum ratio of the component spent on reproduction to the total rate of oxygen consumption, which can be realized by the female reproductive machinery, is called metabolic reproductive efficiency (MRE). We regard MRE as an evolutionary constraint. We demonstrate that MRE may be evaluated for a particular Drosophila phenotype given the fecundity pattern, the age-related pattern of oxygen consumption rate, and the longevity. We use a homeostatic model of aging to simulate a life history of a representative female fly, which describes the control strain in the longterm experiments with the Wayne State Drosophila genotype. We evaluate the theoretically optimal trade-offs in this genotype. Then we apply the Van Noordwijk-de Jong resource acquisition and allocation model, Kirkwood's disposable soma theory, and the Partridge-Barton optimality approach to test if the experimentally observed trade-offs may be regarded as close to the theoretically optimal ones. We demonstrate that the two approaches by Partridge-Barton and Kirkwood allow a positive answer to the question, whereas the Van Noordwijk-de Jong approach may be used to illustrate the optimality. We discuss the prospects of applying the proposed technique to various Drosophila experiments, in particular those including manipulations affecting fecundity.

Metabolic alterations in genetically selected Drosophila strains with different longevities

“…Only a portion of these data have been presented elsewhere and were consistent with our other work showing that extended longevity in our selected strains is dependent on an early up-regulation of the ADS genes (8,9,12).…”

“…Both the Lab and 2Lab strategies are consistent with a shift of energy metabolism from the optimal energy allocations observed in the Ra strain balance of reproduction vs somatic maintenance (12) to a new energy allocation altered in favor of increased somatic maintenance (via high ADS) and decreased reproduction (21, Fig. 8).…”

“…We have empirical evidence showing that inbreeding often eliminates the paraquat resistance of inbred long-lived strains (Arking and Hwangbo, in preparation). In addition, mathematical modeling has demonstrated that our Ra strain has the optimal energy allocations predicted by theory (12). We interpret this fact as indicating that highly inbred animals may not be the best experimental models for every experiment.…”

“…22 for an updated reanalysis of these and related unpublished data, and the additional conclusions to be drawn from it.) Mathematical modeling of the Ra strain's metabolic energy expenditures on reproduction and somatic maintenance suggest that decreasing the energy spent on egg production would significantly increase life span (12). In the case of the La female, increasing the flux through the pentose shunt and using the reduced NADPH generated therein to oxidize the ADS enzymes instead of being used to generate more ATP, represents an increase in the amount of energy being used for somatic maintenance.…”

“…These control strains were deliberately kept under non-selective conditions so as to maintain (more or less) their original state (6) while the Ma and Mb strains were kept under selective conditions for a normal lifespan. Our initial assumption that these R animals represented an optimal mix of life history characteristics is supported by recent mathematical modeling (12). In addition, we used the La and Lb strains to generate by reverse selec'don t~e normal-lived RevLa and RevLb strains (8,9).…”