Collaborative Research: Causes of Parallel Molecular Evolution

分子进化始于DNA的随机变化，但随后自然选择消除了一些变化，保留了其他变化。一个重要的问题涉及到不同物种对类似环境挑战的适应；他们会通过相似还是不同的DNA变化来实现这一点？这个项目将探讨进化的原因，并通过研究生活在安第斯山脉高海拔的鸟类及其低海拔的近亲来预测进化变化的可能性。该项目将探索在不同的大气条件(高海拔和低海拔)下，血红蛋白(血液中携带氧气的蛋白质)如何发生变化，以实现氧气的摄取和释放。该项目将为博士后和研究生提供跨学科的培训，并包括一个公共宣传部分，重点是“适应极端环境”，向小学生传授如何通过自然选择进行进化。所有数据和样本都将与西南生物博物馆(美国新墨西哥州)的标本凭证相关联，并将通过开放访问的数据库进行访问。该项目旨在评估平行分子进化的普遍性，并通过研究独立定居在高海拔环境中的多个物种的血红蛋白(Hb)适应机制来测试关于其原因的假设。对Hb功能的实验分析将被用来识别和描述多种鸟类Hb-O2亲和力进化变化的分子基础，这些物种在安第斯山脉具有不同的海拔范围限制。比较将涉及多个在系统发育上复制的“分类群对”(原产于高海拔或低海拔地区的同种种群或密切相关物种对)。在高海拔和低海拔分类群的功能不同的Hb通过多个氨基酸替换来区分的情况下，将结合定点突变和祖先蛋白复活来检查连接祖先(低亲和力)Hb和衍生(高亲和力)Hb的所有可能途径中顺序突变步骤的功能影响。除了测量每个工程Hb突变体的氧合特性外，还将测量可能与Hb-O2亲和力权衡的额外功能和结构特性。通过将定点突变实验的结果与Hb功能在系统发育中复制的变化联系起来，这种蛋白质工程分析将阐明多效性限制在促进平行分子进化中的作用。

Molecular evolution starts from random changes in DNA, but then natural selection eliminates some of the changes and retains the others. An important question concerns the adaptation of different species to a similar environmental challenge; would they do it through similar or different changes to the DNA? This project will address the causes of evolution, and the possibility to predict evolutionary change by studying birds living at high altitude in the Andes, and their close relatives living at low altitudes. The project will explore the ways in which the hemoglobins (the oxygen carrying proteins of the blood) have changed to enable the uptake and release of oxygen under different atmospheric conditions (high and low altitude). This project will provide interdisciplinary training for postdoctoral and graduate students and includes a public outreach component that will focus on 'adaptation to extreme environments' to teach elementary school students how evolution by natural selection works. All data and samples will be linked to specimen-vouchers at the Museum of Southwestern Biology (U. New Mexico) and will be accessible through an open-access data repository. This project is designed to assess the pervasiveness of parallel molecular evolution and to test hypotheses about its causes by examining mechanisms of hemoglobin (Hb) adaptation in multiple species that have independently colonized high-altitude environments. Experimental analyses of Hb function will be used to identify and characterize the molecular basis of evolved changes in Hb-O2 affinity in multiple bird species that have contrasting altitudinal range limits in the Andes. The comparisons will involve multiple phylogenetically replicated 'taxon pairs' (pairs of conspecific populations or closely related species that are native to high- or low-altitude). In cases where functionally distinct Hbs of high- and low-altitude taxa are distinguished by multiple amino acid substitutions, a combination of site-directed mutagenesis and ancestral protein resurrection will be used to examine the functional effects of sequential mutational steps in all possible pathways that connect the ancestral (low-affinity) Hb and the derived (high-affinity) Hb. In addition to measuring oxygenation properties of each engineered Hb mutant, additional functional and structural properties that can potentially trade-off with Hb-O2 affinity will also be measured. By relating the results of the site-directed mutagenesis experiments to phylogenetically replicated changes in Hb function, this protein-engineering analysis will illuminate the role of pleiotropic constraints in promoting parallel molecular evolution.