Rosenfeld Jordan, Van Leeuwen Travis, Richards Jeffrey, Allen David
Conservation Science Section, B.C. Ministry of Environment, University of British Columbia, 2202 Main Mall, Vancouver, BC, V6T 1Z4, Canada.
Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, BC, V6T 1Z4, Canada.
J Anim Ecol. 2015 Jan;84(1):4-20. doi: 10.1111/1365-2656.12260. Epub 2014 Aug 4.
Mass-specific standard metabolic rate (SMR, or maintenance metabolism) varies greatly among individuals. Metabolism is particularly sensitive to variation in food consumption and growth creating the potential for significant bias in measured SMR for animals that are growing (e.g. juveniles) or of uncertain nutritional status. Consequently, interpreting individual variation in metabolism requires a sound understanding of the potentially confounding role of growth and the relative importance of fixed (genetic) vs. environmental drivers of SMR variation. We review the role of growth in measured SMR variation in juvenile salmonids, with the goals of (i) understanding the contribution of growth (and food consumption) to SMR variation through ontogeny, (ii) understanding the relative contributions of tissue maintenance and biosynthesis (overhead costs of growth) to apparent SMR variation, and (iii) using intrinsic growth effects on SMR to model how alternate life-history strategies may influence growth and measured SMR in juvenile salmonids. SMR measures on juveniles, even when post-absorptive, may be inflated by delayed growth-associated overhead costs, unless juveniles are on a maintenance ration (i.e. not growing). Empirical measurements of apparent SMR in food restricted vs. satiated 2-5 g juvenile salmon demonstrate that estimates may be inflated by as much as 67% due to delayed overhead costs of growth, even when SMR measurements are taken 35 h post-feeding. These results indicate that a substantial component of variation in apparent SMR among juvenile salmonids may be associated with (i) environmentally driven variation in ration (where elevated SMR measurements are an artefact of delayed growth overhead costs), (ii) intrinsic (genetic) or plastic organ-system trade-offs related to increasing investment in metabolically expensive digestive tissue responsible for processing food and (iii) intrinsic (genetic) variation in maximum body size and growth among individuals or life-history types. We suggest that selection for differences in adult body size among resident and anadromous forms leading to differences in juvenile growth trajectories may contribute to both SMR variation and habitat segregation in freshwater, where juveniles with higher growth are constrained to foraging in high velocity habitats to meet their greater consumption needs.
单位体重标准代谢率（SMR，即维持代谢）在个体之间差异很大。代谢对食物消耗和生长的变化特别敏感，这使得对于正在生长的动物（如幼体）或营养状况不确定的动物，所测量的SMR可能存在显著偏差。因此，解释代谢的个体差异需要充分理解生长可能产生的混淆作用以及SMR变化的固定（遗传）驱动因素与环境驱动因素的相对重要性。我们回顾了生长在幼年鲑科鱼类所测量的SMR变化中的作用，目标是：（i）了解生长（和食物消耗）在个体发育过程中对SMR变化的贡献；（ii）了解组织维持和生物合成（生长的间接成本）对表观SMR变化的相对贡献；（iii）利用生长对SMR的内在影响来模拟不同的生活史策略可能如何影响幼年鲑科鱼类的生长和所测量的SMR。即使在吸收后，幼体的SMR测量值也可能因与生长相关的延迟间接成本而被高估，除非幼体处于维持日粮水平（即不生长）。对体重2 - 5克的食物受限与饱腹状态下的幼年鲑鱼表观SMR的实证测量表明，即使在喂食后35小时进行SMR测量，由于生长的延迟间接成本，估计值可能会被高估多达67%。这些结果表明，幼年鲑科鱼类表观SMR变化的很大一部分可能与以下因素有关：（i）环境驱动的日粮变化（其中较高的SMR测量值是生长延迟间接成本的假象）；（ii）与增加对负责处理食物的代谢昂贵的消化组织的投资相关的内在（遗传）或可塑性器官系统权衡；（iii）个体或生活史类型之间最大体型和生长的内在（遗传）差异。我们认为，在定居型和溯河洄游型成年个体体型差异的选择导致幼年生长轨迹不同，并可能导致淡水环境中的SMR变化和栖息地隔离，其中生长较快的幼体被限制在高速栖息地觅食以满足其更大的消耗需求。
