Organisms often encounter varying environments which prompt them to exhibit phenotypic plasticity as a adaptive mechanism. This phenotypic plasticity allows the modification of plastic traits to enhance organismal fitness within a given environment, thus altering correlations between various phenotypic traits. Life-history traits are one of many traits which show plasticity in the face of a changing environment. Body size, lifespan, fertility, and stress resistance such as starvation and desiccation resistance are among the most important life-history traits. These traits show phenotypic, physiological and genetic correlations often manifesting as trade-offs, but can also lead to positive correlations under certain conditions. Previously, studies have shown a trade-off between lifespan and reproduction, and positive correlations in body size and fertility, body size and lifespan, and in body size and stress resistance under different nutritional environments. A key aspect of organismal life-history evolution is to acquire and allocate the energy derived from nutrients across different life stages which are necessary for growth, development and maintenance of vital functions. This distribution of energy primarily dictates the extent and direction of trait correlations including trade-offs. Prior research has primarily investigated the influence of nutrition in regulating trait correlations, by manipulating macronutrient composition in the diet at a specific organismal life stage. However, the impact of such dietary manipulation in conjunction with their nutrient availability at different life stages on these trait correlations is not very well understood.
In our study, we aim to address the cross-talk of stage specific dietary manipulation on trait correlations using the holometabolous insect model, Drosophila melanogaster. We have measured adult traits such as body size, fertility, lifespan, starvation resistance and desiccation resistance under four distinct nutritional regimes consisting of two isocaloric diets (protein-rich and carbohydrate-rich) for each of the larval and adult stages in a full-factorial experimental design. Our findings shows the disruption of canonical correlations between life-history traits. Firstly, a carbohydrate rich larval diet promotes increased body size but fails to correspondingly enhance the fertility. Secondly, the classic trade-off between lifespan and reproduction is disrupted in flies fed with protein-rich adult diet. Finally, the trade-off between body size and lifespan is broken in flies fed with protein-rich adult diet. This study contributes valuable insights into the complex interaction between stage-specific diet and life-history traits. In conclusion, the exploration of correlations among life-history traits and the influence of stage-specific dietary manipulation on these correlations, highlights the complexity of biological systems and emphasizes the need for interdisciplinary approaches to unravel them.