Environmental temperature alters the overall digestive energetics and differentially affects dietary protein and lipid use in a lizard

Processing food (e.g. ingestion, digestion, assimilation) requires energy referred to as specific dynamic action (SDA) and is at least partially fuelled by oxidation of the nutrients (e.g. proteins and lipids) within the recently ingested meal. In ectotherms, environmental temperature can affect the magnitude and/or duration of SDA, but likely also alters the mixture of nutrients that are oxidized to cover these costs. Here, we examined metabolic rate, gut passage time, assimilation efficiency, and fuel use in the lizard Agama atra digesting cricket meals at three ecologically relevant temperatures (20, 25, and 32&[deg]C). Crickets were isotopically enriched with 13C-leucine or 13C-palmitic acid tracers to distinguish between protein and lipid oxidation, respectively. Our results show that higher temperatures increased the magnitude of the peak SDA (by 318% between 32 and 20&[deg]C) and gut passage rate (63%), and decreased the duration of the SDA response (20% for males and 48%...食物处理过程（如摄食、消化、同化作用）所需的能量被称为特殊动力作用（specific dynamic action, SDA），其至少部分由新近摄入食物中的营养素（如蛋白质与脂质）氧化供能。对于变温动物（ectotherms）而言，环境温度不仅会影响SDA的强度和/或持续时长，还可能改变用于补偿该能量消耗的氧化营养素组成。本研究针对三种生态相关温度（20℃、25℃、32℃）下消化蟋蟀食物的阿特拉鬣蜥（Agama atra），探究了其代谢率、肠道通过时间、同化效率以及供能底物的使用情况。实验所用蟋蟀分别通过13C-亮氨酸（13C-leucine）或13C-棕榈酸（13C-palmitic acid）示踪剂进行同位素富集，以分别区分蛋白质与脂质的氧化过程。研究结果表明，更高的温度会提升SDA峰值强度（32℃与20℃之间提升318%）与肠道通过速率（提升63%），并缩短SDA响应的持续时长（雄性缩短20%，雌性缩短48%...