Nutritional Trade-Offs in <i>Drosophila</i>

Animals often regulate their nutrient intake according to physiological needs. There is evidence that different traits require specific nutrient blends, and that animals cannot always maximise all traits with a single diet (‘nutritional trade-offs’). However, we still do not have a clear understanding of which traits might be involved in nutritional trade-offs. I compiled data from the Geometric Framework of nutrition literature on the ratio of protein and carbohydrates that maximise (best PC ratios) or minimise (worst PC ratios) several larval and adult traits in Drosophila melanogaster. Best and worst PC ratios clustered into three regions in the protein-carbohydrate nutrient space: (1) Low PC ratios (1:8 or higher) are best for lifespan but worst for growth or reproductive traits; (2) High PC ratios (1:1 or lower) are best for adult body mass, male reproduction and larval developmental time but worst for lifespan; (3) Intermediate PC ratios (between 1:1 and 1:8) are best for female lifetime egg production, female reproductive rate and larval survival. These findings support lifespan-reproduction nutritional trade-offs, highlight the potential for metamorphosis to solve nutritional trade-offs across life stages, and the potential for intralocus sexual conflict to emerge over the expression of metabolic genes.