Data from: Integrating lipid storage into general representations of fish energetics

Fish, even of the same species, can exhibit substantial variation in energy density (energy per unit wet weight). Most of this variation is due to differences in the amount of storage lipids. In addition to their importance as energy reserves for reproduction and for survival during unfavourable conditions, the accumulation of lipids represents a large energetic flux for many species, so figuring out how this energy flux is integrated with other major energy fluxes (growth, reproduction) is critical for any general theory of organismal energetics. Here, we synthesize data from a wide range of fish species and identify patterns of intraspecific variation in energy storage, and use these patterns to formulate a general model of energy allocation between growth, lipid storage and reproduction in fishes. From the compiled data we identified two patterns: (1) energy density increases with body size during the juvenile period, but is invariant with body size within the adult size range for most species, and (2) energy density changes across seasons, with depletion over winter, but increases fastest in periods of transition between favourable and unfavourable conditions for growth (i.e. fall). Based on these patterns we propose DEBlipid, a simple, general model of energy allocation that is closely related to a simplified version of Dynamic Energy Budget theory, DEBkiss. The crux of the model is that assimilated energy is partitioned, with κ fraction of energy allocated to pay maintenance costs first, and the surplus allocated to growth, and 1 − κ fraction of assimilated energy is allocated to accumulating storage lipids during the juvenile phase, and later to reproduction as adults. This mechanism, in addition to capturing the two patterns that motivated the model, was able to predict lipid dynamics in a novel context, the migration of anadromous fish from low-food freshwater to high-food marine environments. Furthermore, the model was used to explain intra and interspecific variation in reproductive output based on patterns of lipid accumulation as juveniles. Our results suggest that many seemingly complex, adaptive energy allocation strategies in response to ontogeny, seasonality and habitat quality can emerge from a simple physiological heuristic.即使是同一物种的鱼类，其能量密度（energy density，单位湿重所含能量）也可能存在显著差异。这类差异大多源于储存脂质（storage lipids）含量的不同。储存脂质不仅是鱼类繁殖以及逆境存活的重要能量储备，对于多数鱼类而言，脂质积累本身也是一项大型能量通量（energetic flux）过程。因此，厘清该能量通量与生长、繁殖等其他主要能量通量的整合机制，对于构建普适性的个体能量学（organismal energetics）理论至关重要。 本研究整合了多类鱼类的相关数据，识别出鱼类能量储存的种内变异（intraspecific variation）模式，并基于这些模式构建了鱼类生长、储存脂质与繁殖间的通用能量分配（energy allocation）模型。 通过汇编所得的数据，我们识别出两类核心模式：其一，多数鱼类的能量密度在幼体期（juvenile period）随体型增大而升高，但在成体体型区间内则无显著体型相关性变化；其二，能量密度随季节发生波动：冬季出现能量耗竭，而在生长条件由优转劣（即秋季）的过渡期，能量密度提升速率最快。 基于上述模式，我们提出了DEBlipid模型——一款简洁通用的鱼类能量分配模型，其核心逻辑与简化版动态能量预算理论（Dynamic Energy Budget, DEBkiss）高度契合。该模型的核心机制为：鱼类将同化获得的能量进行分配：首先以κ比例的能量支付维持代谢成本，剩余能量用于生长；而1−κ比例的同化能量在幼体阶段用于储存脂质积累，成体阶段则转向繁殖投入。该机制不仅复现了构建模型时依据的两类核心模式，还能够在全新场景中预测脂质动态——例如溯河洄游鱼类（anadromous fish）从低食物浓度淡水环境向高食物浓度海洋环境的迁徙过程中的脂质变化。此外，该模型还可基于幼体阶段的脂质积累模式，解释繁殖产出的种内与种间变异。 本研究结果表明，许多看似复杂、针对个体发育（ontogeny）、季节波动与生境质量变化的适应性能量分配策略，均可通过简洁的生理学启发式规则推导得出。