Drosophila disengage systemic protein storage as an evolutionary response to chronic larval malnutrition

Nutritional geometry was used to explore the effects of dietary composition on larval developmental traits in Drosophila melanogaster populations that had been subjected to long-term selection under poorer or richer nutritional conditions. When tested across a range of diets varying systematically in the ratio of protein to carbohydrate (P:C) and energy density, larvae that were adapted to the poorer nutritional condition developed faster to a smaller size with greater pupation success rates than did control larvae under a combination of low-protein and low-carbohydrate dietary conditions that were equivalent to the ancestral diet composition, indicating evolutionary tuning to ensure survival on the poor ancestral diet. Results from measurement of haemolymph storage proteins suggested that larvae that were selected under a poor food environment utilized ingested protein for immediate larval growth, rather than for transcribing haemolymph storage proteins in preparation for adult metamorphosis. Our study illustrates the potential for the nutritional environment to induce selection on life-history traits that span across life stages and demonstrates the utility of the fly as a model for studying the mechanisms underlying adaptation to nutrition transitions.