Additive and context-dependent effects of developmental and adult diet on life-history traits and their associations in outbredDrosophila melanogasterpopulation

Life-history traits such as body size, reproduction, survival, and stress resistance are fundamental to an organism's fitness and are highly influenced by nutritional environments at different life stages. In this study, we used a full factorial experimental design with isocaloric diets varying in protein-to-carbohydrate ratios during both developmental and adult stages to investigate their effects on key life-history traits in an outbred Drosophila melanogaster population. Our results demonstrated significant diet-induced plasticity, with body size predominantly determined by the developmental diet, where flies raised on carbohydrate-rich diets were larger as adults. Fertility, however, was enhanced by protein-rich diets at both developmental and adult stages, emphasizing the role of protein in reproductive success. Lifespan was strongly stage-dependent, with carbohydrate-rich developmental diets extending adult lifespan, while the same diet in adulthood shortened it. Furthermore, starvation resistance was improved by a protein-rich developmental diet, whereas desiccation resistance was enhanced by a carbohydrate-rich adult diet, illustrating distinct stage-specific nutritional effects on stress tolerance. Notably, no interactions were found between developmental and adult diets for any of these traits, suggesting independent and additive effects of nutrition across life stages. Additionally, the relationships between traits, such as body size and fertility or lifespan and reproduction, shifted depending on dietary context, challenging canonical trade-offs and highlighting the plasticity of trait correlations. These findings suggest that the nutritional environment can decouple established life-history trait correlations, contributing to context-dependent evolutionary trajectories. This highlights the need to account for both developmental and adult dietary environments when examining how organisms adapt to changing ecological conditions.