Data from: Temperature dependence of predation stress and the nutritional ecology of a generalist herbivore

Prey at risk of predation may experience stress and respond physiologically by altering their metabolic rates. Theory predicts that such physiological changes should alter prey nutrient demands from N-rich to C-rich macronutrients and shift the balance between maintenance and growth/reproduction. Theory further suggests that for ectotherms, temperature stands to exacerbate this stress. Yet, the interactive effects of predation stress and temperature stress on diet, metabolism, and survival of ectotherms are not well known. This knowledge gap was addressed with a laboratory study in which wild juvenile grasshoppers were collected, assigned to one of three groups, and raised at three different temperatures. All grasshoppers had access to equal quantities of two diets composed of opposite carbohydrate:protein ratios. Half of the individuals in each temperature group were exposed to predation risk cues from spider predators, while the other half were kept in risk free conditions. Grasshoppers consumed more carbohydrates when exposed to predation risk, but consumption favored greater protein intake as temperature increased. Moreover, the difference in carbohydrate intake between risk cue and risk free treatments diminished as temperature increased. Furthermore, variability between individual consumption patterns both within and between treatments decreased markedly as temperature increased, suggesting that higher temperatures promote more consistent individual consumption behaviors. Grasshoppers grew faster and larger as temperature increased, which translated into higher survival rates at higher temperatures. Warmer grasshoppers also did not alter their metabolic rates in response to predation risk cues, in contrast to colder grasshoppers. Digestive efficiency increased with temperature as well, further indicating that lower temperatures were much more stressful than higher temperatures for grasshoppers. The study shows that physiological responses of ectothermic herbivores to predation stress are highly plastic and temperature dependent, with higher temperatures promoting increased protein intake, growth, development, survival, and digestive efficiency relative to colder temperatures. These findings help to reconcile why dietary responses (proportion of protein vs. carbohydrate intake) to predation stress may vary among different prey taxa studied previously.

面临捕食风险的猎物可能会产生应激反应，并通过改变代谢速率产生生理响应。相关理论预测，此类生理变化会使猎物的营养需求从富氮宏量营养素转向富碳宏量营养素，并改变维持代谢与生长/繁殖之间的平衡。进一步的理论表明，对于变温动物（ectotherms）而言，温度可能会加剧这类应激反应。然而，学界目前对捕食应激与温度应激对变温动物的饮食、代谢及存活的交互效应尚不清楚。为填补这一认知空白，本研究通过室内实验展开探究：研究人员采集野生幼年蚱蜢，将其随机分为三组，并在三种不同温度下饲养。所有蚱蜢均可获取等量的两种饲料，这两种饲料的碳水化合物与蛋白质比例恰好相反。每个温度组中，一半个体暴露于蜘蛛捕食者释放的捕食风险线索中，另一半则处于无风险环境中。当面临捕食风险时，蚱蜢会摄入更多碳水化合物，但随着温度升高，其饮食选择更倾向于增加蛋白质摄入。此外，风险线索组与无风险组之间的碳水化合物摄入差异，随温度升高而逐渐缩小。进一步而言，无论组内还是组间，个体饮食模式的变异程度均随温度升高显著降低，这表明更高温度可促使个体饮食行为更具一致性。随着温度升高，蚱蜢的生长速度更快、体型更大，进而在高温环境下存活率更高。与低温环境下的蚱蜢不同，处于温暖环境中的蚱蜢并不会因捕食风险线索而改变其代谢速率。消化效率也随温度升高而提升，这进一步表明，相较于高温环境，低温环境对蚱蜢的应激程度更强。本研究表明，变温植食动物对捕食应激的生理响应具有高度的表型可塑性，且受温度调控：相较于低温环境，高温环境可促进蚱蜢增加蛋白质摄入、提升生长、发育、存活能力与消化效率。本研究结果有助于解释为何此前不同猎物类群对捕食应激的饮食响应（蛋白质与碳水化合物摄入比例）存在差异。