School of Oceanography, University of Washington, Seattle, Washington, United States of America.
Institute of Zoology, University of Cologne, Cologne, Germany.
PLoS Biol. 2024 Jan 16;22(1):e3002443. doi: 10.1371/journal.pbio.3002443. eCollection 2024 Jan.
The minimum O2 needed to fuel the demand of aquatic animals is commonly observed to increase with temperature, driven by accelerating metabolism. However, recent measurements of critical O2 thresholds ("Pcrit") reveal more complex patterns, including those with a minimum at an intermediate thermal "optimum". To discern the prevalence, physiological drivers, and biogeographic manifestations of such curves, we analyze new experimental and biogeographic data using a general dynamic model of aquatic water breathers. The model simulates the transfer of oxygen from ambient water through a boundary layer and into animal tissues driven by temperature-dependent rates of metabolism, diffusive gas exchange, and ventilatory and circulatory systems with O2-protein binding. We find that a thermal optimum in Pcrit can arise even when all physiological rates increase steadily with temperature. This occurs when O2 supply at low temperatures is limited by a process that is more temperature sensitive than metabolism, but becomes limited by a less sensitive process at warmer temperatures. Analysis of published species respiratory traits suggests that this scenario is not uncommon in marine biota, with ventilation and circulation limiting supply under cold conditions and diffusion limiting supply at high temperatures. Using occurrence data, we show that species with these physiological traits inhabit lowest O2 waters near the optimal temperature for hypoxia tolerance and are restricted to higher O2 at temperatures above and below this optimum. Our results imply that hypoxia tolerance can decline under both cold and warm conditions and thus may influence both poleward and equatorward species range limits.
水生动物的最低需氧量通常随着代谢率的加速而随温度升高而增加，但最近对临界氧阈值（“Pcrit”）的测量显示出更复杂的模式，包括在中间热“最佳”处出现最小值。为了辨别这种曲线的普遍性、生理驱动因素和生物地理表现形式，我们使用水生呼吸动物的一般动态模型分析新的实验和生物地理数据。该模型模拟了氧从周围水中通过边界层传递到动物组织的过程，这是由温度依赖的代谢率、扩散气体交换以及具有 O2-蛋白质结合的通气和循环系统驱动的。我们发现，即使所有生理速率都随温度稳定增加，Pcrit 也可能出现热最优。当低温下的 O2 供应受到比代谢更敏感的过程限制，但在较温暖的温度下受到不太敏感的过程限制时，就会发生这种情况。对已发表物种呼吸特征的分析表明，这种情况在海洋生物群中并不罕见，在寒冷条件下，通气和循环限制供应，而在高温下扩散限制供应。使用出现数据，我们表明具有这些生理特征的物种栖息在缺氧耐受性最佳温度附近的最低 O2 水域中，并且在该最佳温度以上和以下的温度下受到限制，只能生活在高 O2 水域中。我们的结果意味着在寒冷和温暖的条件下，缺氧耐受性都可能下降，因此可能会影响极地和赤道物种的分布范围限制。
