University of Texas at Austin, Marine Science Institute, Port Aransas, TX 78373, USA.
J Exp Biol. 2021 Jul 1;224(13). doi: 10.1242/jeb.232520. Epub 2021 Jun 29.
The metabolic index concept combines metabolic data and known thermal sensitivities to estimate the factorial aerobic scope of animals in different habitats, which is valuable for understanding the metabolic demands that constrain species' geographical distributions. An important assumption of this concept is that the O2 supply capacity (which is equivalent to the rate of oxygen consumption divided by the environmental partial pressure of oxygen: ) is constant at O2 tensions above the critical O2 threshold (i.e. the where O2 uptake can no longer meet metabolic demand). This has led to the notion that hypoxia vulnerability is not a selected trait, but a by-product of selection on maximum metabolic rate. In this Commentary, we explore whether this fundamental assumption is supported among fishes. We provide evidence that O2 supply capacity is not constant in all fishes, with some species exhibiting an elevated O2 supply capacity in hypoxic environments. We further discuss the divergent selective pressures on hypoxia- and exercise-based cardiorespiratory adaptations in fishes, while also considering the implications of a hypoxia-optimized O2 supply capacity for the metabolic index concept.
代谢指数的概念结合了代谢数据和已知的热敏感性，以估计不同生境中动物的因子有氧范围，这对于理解限制物种地理分布的代谢需求很有价值。这一概念的一个重要假设是，在临界氧阈值以上的氧张力下（即氧摄取量不再满足代谢需求的地方），氧供应能力（相当于耗氧量除以环境氧分压： ）是恒定的。这导致了这样一种观点，即低氧脆弱性不是一个被选择的特征，而是对最大代谢率选择的副产品。在这篇评论中，我们探讨了这一基本假设在鱼类中是否成立。我们提供的证据表明，并不是所有鱼类的氧供应能力都是恒定的，有些鱼类在低氧环境中表现出较高的氧供应能力。我们进一步讨论了鱼类在低氧和运动基础上的心肺适应的不同选择压力，同时也考虑了优化的低氧氧供应能力对代谢指数概念的影响。
