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%...