Data from: Macronutrient balance modulates the temperature-size rule in an ectotherm

Most ectotherms mature at a larger body size in colder conditions, a phenomenon known as the temperature-size rule (TSR). While a number of hypotheses have been proposed to explain this rule, little work has been done to understand the TSR from a nutritional perspective. We used the final-instar caterpillars of Spodoptera litura to investigate how dietary protein:carbohydrate (P:C) balance influences the relationship between temperature and body size. The strength and direction of the thermal reaction norm for body size were significantly altered by dietary P:C balance. The slope of the reaction norm was near flat for caterpillars raised on a balanced food (P:C=1:1), but significantly negative for those on nutritionally imbalanced foods (1:5 or 5:1), especially when carbohydrate was in considerable excess. Body lipid reserves were mainly responsible for this size differences. When allowed to choose between imbalanced diets, caterpillars increased their preference for carbohydrate to meet high energy demand at higher temperatures. This temperature-driven shift in nutrient preference resulted in a significant reduction of the slope of the TSR, with body lipid reserves being maintained to a similar level across temperatures. These results highlight the importance of macronutrient balance as a modulator shaping the relationship between temperature and body size in ectotherms.