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

蜂鸟是特殊的，因为它们的体型小，代谢率高，飞行模式消耗能量。这些特征似乎使蜂鸟不适合恶劣的，缺氧的，高海拔的环境。巧合的是，蜂鸟在赤道的安第斯山脉达到其多样性的顶峰，超过80种蜂鸟达到3000米或更高的海拔。蜂鸟大约在3500万年前进化，远在安第斯山脉开始上升之前。随着安第斯山脉的隆起，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，以确定过去的选择，可能伴随着进化的海拔变化的证据。独立的高海拔人群已经进化出独特的适应性呼吸策略，但它是未知的替代策略是否反映殖民时间或不同的进化轨迹的差异。蜂鸟代表了一个理想的系统，在其中评估这些替代品，因为独立的谱系经历了高海拔殖民在交错的时间在过去的1500万至2000万年。我们将描述蜂鸟血红蛋白和肌红蛋白基因型，并测量几个血液学参数，盘旋代谢率，和缺氧耐受性的一套物种，跨越5000米的海拔梯度。这些结果将使我们更好地理解高海拔呼吸、血红蛋白的进化和病理，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NSF的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.