Context-dependent effects of developmental and adult diet on life-history traits in <i>Drosophila melanogaster</i>

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 across life stages. In this study, we employed a full factorial experimental design to investigate the effects of isocaloric diets (diets with equal caloric content but differing macronutrient composition) on key life-history traits in an outbred Drosophila melanogaster population. Our results demonstrated significant diet-induced plasticity, with males reared on carbohydrate-rich developmental diets had larger wings as adults. Fertility increased with protein-rich diets at both developmental and adult stages, reaffirming the critical role of dietary protein in enhancing reproductive success. Lifespan exhibited sexually dimorphic responses: carbohydrate-rich developmental diets extended male lifespan, while carbohydrate-rich adult diets reduced lifespan in both sexes. Stress resistance traits, including starvation and desiccation resistance, were unaffected by developmental diets but influenced by adult diets, with carbohydrate-rich adult diets enhancing survival under both stress conditions in males and females. While most traits exhibited additive effects of nutrition across life stages, a marginal interaction for male starvation resistance suggests that developmental and adult diets can interact in a trait- and sex-specific manner. Moreover, associations between dietary effects on life-history traits were context-dependent, driven primarily by adult diets and varying by sex. These findings emphasize the role of stage-specific nutritional environments in modulating life-history traits and their correlations, offering insights into how organisms may adapt to changing ecological conditions and the importance of considering both developmental and adult dietary contexts in evolutionary studies.