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.绝大多数变温动物（ectotherms）在低温环境下会发育至更大体型，这一现象被称为温度体型规则（temperature-size rule, TSR）。尽管已有诸多假说被提出以解释该规则，但从营养视角解析TSR的研究仍较为匮乏。本研究以斜纹夜蛾（Spodoptera litura）的末龄幼虫为实验材料，探究膳食蛋白质与碳水化合物（P:C）的比例平衡如何调控温度与体型间的关联。膳食P:C比例显著改变了体型热反应规范的强度与方向：在营养均衡饲料（P:C=1:1）上饲养的幼虫，其热反应规范斜率接近平坦；而在营养失衡饲料（1:5或5:1）上饲养的幼虫，斜率则显著为负，尤其当碳水化合物过量时这一效应更为突出。幼虫体内的脂质储备差异是导致体型差异的主要原因。当允许幼虫在失衡饲料间进行选择时，它们会提升对碳水化合物的偏好，以满足高温环境下的高能量需求。这种由温度驱动的营养偏好转变，显著降低了TSR的斜率，并使得不同温度下的体内脂质储备维持在相近水平。上述研究结果凸显了大量营养素（macronutrient）平衡作为调节因子，在塑造变温动物体温与体型间关联中的重要意义。