Martin Benjamin T, Heintz Ron, Danner Eric M, Nisbet Roger M
Cooperative Institute for Marine Ecosystems and Climate (CIMEC), University of California, 1156 High St, Santa Cruz, CA, 95064, USA.
Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanographic and Atmospheric Administration, 110 Shaffer Road, Santa Cruz, CA, 95060, USA.
J Anim Ecol. 2017 Jul;86(4):812-825. doi: 10.1111/1365-2656.12667. Epub 2017 May 8.
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.
鱼类，即使是同一物种，其能量密度（每单位湿重的能量）也可能表现出显著差异。这种差异大多归因于储存脂质数量的不同。脂质不仅作为繁殖和在不利条件下生存的能量储备至关重要，对于许多物种而言，脂质的积累还代表着大量的能量通量，因此弄清楚这种能量通量如何与其他主要能量通量（生长、繁殖）整合，对于任何生物能量学的通用理论都至关重要。在此，我们综合了来自广泛鱼类物种的数据，确定了种内能量储存的变异模式，并利用这些模式构建了一个关于鱼类生长、脂质储存和繁殖之间能量分配的通用模型。从汇编的数据中我们识别出两种模式：（1）幼年期能量密度随体型增大而增加，但对于大多数物种而言，在成体体型范围内能量密度不随体型变化；（2）能量密度随季节变化，冬季能量消耗，但在生长有利和不利条件转换期间（即秋季）增加最快。基于这些模式，我们提出了DEBlipid，这是一个简单的通用能量分配模型，与动态能量预算理论的简化版本DEBkiss密切相关。该模型的关键在于，同化能量被分配，其中κ部分能量首先用于支付维持成本，剩余部分用于生长，而在幼年期，1 - κ部分的同化能量用于积累储存脂质，成年后则用于繁殖。这种机制除了捕捉到推动模型构建的两种模式外，还能够在一个新的情境中预测脂质动态，即溯河洄游鱼类从低食物量的淡水环境向高食物量的海洋环境的洄游。此外，该模型还用于根据幼年期脂质积累模式解释繁殖输出的种内和种间变异。我们的结果表明，许多看似复杂的、针对个体发育、季节性和栖息地质量的适应性能量分配策略可能源自一种简单的生理启发式机制。
