Data from: Cold-adaptation increases rates of nutrient flow and metabolic plasticity during cold exposure in (Drosophila melanogaster)

Metabolic flexibility is an important component of adaptation to stressful environments, including thermal stress and latitudinal adaptation. A long history of population genetic studies suggest that selection on core metabolic enzymes may shape life histories by altering metabolic flux. However, the direct relationship between selection on thermal stress hardiness and metabolic flux has not previously been tested. We investigated flexibility of nutrient catabolism during cold stress in Drosophila melanogaster artificially selected for fast or slow recovery from cold-coma (cold-hardy and -susceptible), specifically testing the hypothesis that stress adaptation affects metabolic flux. Using 13C-labeled glucose, we first showed that cold-hardy flies more rapidly incorporate ingested carbon into amino acids and newly synthesized glucose, permitting synthesis of protective molecules essential for resisting cold stress. Second, using glucose and leucine tracers we showed that cold-hardy flies had higher oxidation rates than cold-susceptible flies before cold exposure, greater metabolic suppression during the cold-stress exposure, and returned to higher oxidation rates during recovery. Increased plasticity in substrate catabolism may allow cold-adapted flies to resist gradual loss of metabolic homeostasis in the cold, by suppressing substrate catabolism during cold exposure and thus maintaining energy balance in the face of reduced demand. This work illustrates for the first time the differences in nutrient fluxes that underpin cold adaptation, suggesting that metabolic costs associated with cold hardiness could invoke resource-based trade-offs that shape life histories.

代谢灵活性（metabolic flexibility）是应对各类胁迫环境（包括温度胁迫与纬度适应性）的关键适应性组分。长期以来的群体遗传学研究表明，对核心代谢酶的选择可通过改变代谢通量（metabolic flux）塑造生物的生活史策略。然而，此前尚未有研究验证温度胁迫抗性选择与代谢通量之间的直接关联。我们以经人工选育、可快速或缓慢从冷昏迷中恢复的黑腹果蝇（Drosophila melanogaster）（分为抗寒型与寒敏感型）为研究对象，探究其在冷胁迫过程中的营养分解代谢灵活性，专门验证“胁迫适应性会影响代谢通量”这一假说。首先，利用13C标记葡萄糖（13C-labeled glucose）开展实验，我们发现抗寒型果蝇可将摄入的碳更快速地整合进入氨基酸与新合成的葡萄糖中，从而合成抵御冷胁迫所需的保护性分子；其次，通过葡萄糖与亮氨酸示踪剂，我们观测到：冷暴露前，抗寒型果蝇的氧化速率高于寒敏感型果蝇；冷胁迫暴露期间，其代谢抑制程度更强；而在恢复阶段则可回升至更高的氧化速率。底物分解代谢的可塑性提升，可使冷适应果蝇通过在冷暴露阶段抑制底物分解代谢，在需求降低的前提下维持能量平衡，进而抵御冷环境下代谢稳态的逐步丧失。本研究首次阐明了支撑冷适应性的营养通量差异，表明与抗寒性相关的代谢成本可能引发基于资源的权衡效应，进而塑造生物的生活史策略。