Storz Jay F
School of Biological Sciences, University of Nebraska, Lincoln, NE 68588, USA
J Exp Biol. 2016 Oct 15;219(Pt 20):3190-3203. doi: 10.1242/jeb.127134.
In air-breathing vertebrates at high altitude, fine-tuned adjustments in hemoglobin (Hb)-O affinity provide an energetically efficient means of mitigating the effects of arterial hypoxemia. However, it is not always clear whether an increased or decreased Hb-O affinity should be expected to improve tissue O delivery under different degrees of hypoxia, due to the inherent trade-off between arterial O loading and peripheral O unloading. Theoretical results indicate that the optimal Hb-O affinity varies as a non-linear function of environmental O availability, and the threshold elevation at which an increased Hb-O affinity becomes advantageous depends on the magnitude of diffusion limitation (the extent to which O equilibration at the blood-gas interface is limited by the kinetics of O exchange). This body of theory provides a framework for interpreting the possible adaptive significance of evolved changes in Hb-O affinity in vertebrates that have colonized high-altitude environments. To evaluate the evidence for an empirical generalization and to test theoretical predictions, I synthesized comparative data in a phylogenetic framework to assess the strength of the relationship between Hb-O affinity and native elevation in mammals and birds. Evidence for a general trend in mammals is equivocal, but there is a remarkably strong positive relationship between Hb-O affinity and native elevation in birds. Evolved changes in Hb function in high-altitude birds provide one of the most compelling examples of convergent biochemical adaptation in vertebrates.
在高海拔地区的空气呼吸脊椎动物中，血红蛋白（Hb）与氧气亲和力的精细调节提供了一种能量高效的方式来减轻动脉血氧不足的影响。然而，由于动脉血氧装载和外周血氧卸载之间存在固有的权衡，在不同程度的缺氧情况下，增加或降低Hb与氧气的亲和力是否能改善组织氧气输送并不总是明确的。理论结果表明，最佳的Hb与氧气亲和力随环境氧气可用性的非线性函数而变化，而Hb与氧气亲和力增加变得有利的阈值升高取决于扩散限制的程度（氧气在血气界面平衡受氧气交换动力学限制的程度）。这一理论体系为解释在已适应高海拔环境的脊椎动物中，Hb与氧气亲和力进化变化可能的适应性意义提供了一个框架。为了评估经验概括的证据并检验理论预测，我在系统发育框架中综合了比较数据，以评估哺乳动物和鸟类中Hb与氧气亲和力和原生海拔之间关系的强度。哺乳动物中普遍趋势的证据并不明确，但鸟类中Hb与氧气亲和力和原生海拔之间存在非常强的正相关关系。高海拔鸟类血红蛋白功能的进化变化是脊椎动物趋同生化适应最引人注目的例子之一。
