The Phylogenetic and Biogeographic History of High Altitude Adaptation in Hummingbirds: Selection on Hemoglobin Proteins as a Function of Oxygen Supply and Demand

蜂鸟的特殊之处在于它们体型小，代谢率高，飞行方式耗费能量。这些特征似乎使蜂鸟不适合恶劣的、缺氧的高海拔环境。矛盾的是，蜂鸟的多样性在赤道安第斯山脉达到顶峰，超过80种蜂鸟到达海拔3000米或更高的高度。蜂鸟大约在3500万年前进化，远在安第斯山脉开始上升之前。在安第斯山脉隆起后，许多独立的蜂鸟谱系在高海拔栖息地定居，这些入侵伴随着血红蛋白的变化，血红蛋白是负责摄取和输送氧气的呼吸蛋白。这项研究将检查275种蜂鸟的血红蛋白基因，以确定过去可能伴随着海拔进化变化而进行的选择的证据。独立的高海拔人类种群进化出了独特的适应性呼吸策略，但尚不清楚替代策略是否反映了殖民时间的差异或明显的进化轨迹。蜂鸟是评估这些选择的理想系统，因为在过去的1500-2000万年里，独立的谱系在交错的时间里经历了高海拔的殖民。我们将确定蜂鸟的血红蛋白和肌红蛋白的基因类型，并测量跨越5000米海拔梯度的一组物种的几个血液学参数、徘徊代谢率和耐缺氧能力。这些结果将加深我们对高海拔呼吸、血红蛋白进化和病理学的理解，以及决定论和偶然性在进化中的相对作用。这项研究的部分资金由美国国家科学基金会国际科学与工程办公室提供。

Hummingbirds are exceptional for their small body size, high metabolic rate, and energetically costly mode of flight. These characteristics would seem to make hummingbirds ill-suited for harsh, oxygen-depleted, high-altitude environments. Paradoxically, hummingbirds reach their peak diversity in the equatorial Andes, and over 80 species reach elevations of 3000m or higher. Hummingbirds evolved about 35 million years ago, well before the Andes began ascending. Following Andean uplift, numerous independent hummingbird lineages colonized high-altitude habitats, and these invasions were accompanied by changes in hemoglobin, the respiratory protein responsible for uptake and delivery of oxygen. This research will examine hemoglobin genes for 275 hummingbird species in order to identify evidence of past selection that may have accompanied evolutionary shifts in elevation.Independent high-altitude human populations have evolved unique adaptive respiratory strategies, but it is unknown whether alternative strategies reflect differences in timing of colonization or distinct evolutionary trajectories. Hummingbirds represent an ideal system in which to evaluate these alternatives because independent lineages have undergone high-altitude colonization at staggered times over the last 15-20 million years. We will characterize hummingbird hemoglobin and myoglobin genotypes, and measure several hematological parameters, hovering metabolic rates, and hypoxia tolerance for a suite of species that span a 5000m elevational gradient. The results will refine our understanding of high-altitude respiration, hemoglobin evolution and pathology, and the relative roles of determinism and contingency in evolution. Partial funding for this study was provided by the Office of International Science and Engineering at NSF.