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. While a number of hypotheses have been proposed to explain this rule, little work has been done to understand it from a nutritional perspective. We have 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 nearly flat for caterpillars raised on a balanced food () but was significantly negative for those on nutritionally imbalanced foods (1∶5 or 5∶1), especially when carbohydrates were in considerable excess. These nutrient-dependent effects of temperature on body size were caused mainly by corresponding changes in body lipid storage. When allowed to choose between imbalanced diets, caterpillars increased their preference for carbohydrates to meet high energy demands at higher temperatures. The slope of the thermal reaction norm for body size was substantially reduced by such a temperature-driven shift in nutrient preference, indicating that the impact of high temperature on body size was buffered by altered food selection. This study highlights the importance of macronutrient balance as a key factor modulating the relationship between temperature and body size in ectotherms and provides a novel approach for understanding the temperature-size rule.绝大多数变温动物（ectotherms）在低温环境下成熟时体型更大，这一现象被称为温度-体型规则（temperature-size rule）。尽管已有诸多假说被提出以解释该规则，但从营养视角探究其成因的研究却寥寥无几。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∶碳水化合物（P∶C）比对温度与体型间关系的影响。膳食P∶C比显著改变了体型热反应规范（thermal reaction norm）的强度与方向。以均衡膳食饲养的幼虫，其热反应规范斜率近乎平缓；而以营养失衡膳食（1∶5或5∶1）饲养的幼虫，斜率则显著为负，尤其当碳水化合物过量较多时。温度对体型的这种依赖营养的效应，主要源于体内脂质储存的相应变化。当允许幼虫选择失衡膳食时，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，大幅降低了体型热反应规范的斜率，表明高温对体型的影响可通过改变食物选择得到缓冲。本研究强调了大量营养素平衡（macronutrient balance）作为调节变温动物温度与体型关系的关键因子的重要性，并为理解温度-体型规则提供了全新的研究路径。