Post glacial reticulate evolution: phylogeography of Packera in western North America

Packera是菊科菊科植物50多种的一个属，是研究北美植物区系进化史的理想类群，因为(I)它广泛存在于北美，物种分布在所有主要的生物群中；(Ii)由于明显的杂交和渐渗，许多物种的定义很模糊，因此杂交模式和由此产生的基因流动都可以在一系列历史和地理背景下进行研究；(Iii)高水平的种群内叶绿体DNA(CpDNA)单倍型多样性提供了一个可以在系统发育背景下分析的分子标记来源。帕克拉起源于墨西哥，并在那里、大平原、北极和北美西海岸实现了多元化。我们将研究所有这些地区的进化模式，以更好地评估地理隔离、自然选择、杂交、避难生存和物种迁徙在植物区系进化中的作用。我们将检查帕克拉分叉的两个墨西哥山脉的核和cpDNA的分子差异，以确定这是否可以解释在许多北部类群中观察到的cpDNA多样性的基础。在北极，我们将评估避难所生存的重要性，然后是迁徙和最近的杂交，而在大平原，我们认为广泛存在的物种显示出高度单倍型多样性的模式，这可能可以在冰川后迁徙模式和新重叠物种之间的杂交背景下解释。在西海岸，有两个因素似乎很重要：(I)蛇纹岩土壤通过对殖民者对土壤的耐受性进行选择，塑造了包括帕克拉在内的许多植物群体的进化；(Ii)各种沿海避难所可能为整个区域的冰川后殖民物种提供了遗传多样性的来源。我们在未来五年对帕克拉的系统地理研究，将提高我们对所有这些因素的进化重要性的理解，从而极大地提高我们对影响北美植物区系演化的因素的理解。

Packera, a genus of 50+ species in the Asteraceae (Daisy) family, is an ideal group for studies aimed at understanding the evolutionary history of the North American flora because (i) it is widespread in North America, with species occurring in all the major biomes (ii) many of the species are poorly defined due to apparent hybridization and introgression so that patterns of hybridization and resulting gene flow can both be examined in a range of historical and geographical contexts and (iii) high levels of intrapopulational chloroplast DNA (cpDNA) haplotype diversity provide a source of molecular markers than can be analyzed in a phylogenetic context. Packera originated in Mexico and has diversified there, in the Great Plains, the arctic and along the North American west coast. We will examine evolutionary patterns in all these regions to better assess the role of geographical isolation, natural selection, hybridization, refugial survival and species migration in the evolution of the flora. We will examine molecular divergence of both nuclear and cpDNA from the two Mexican mountain ranges where Packera diverged to determine whether this, followed by northern migration and widespread hybridization would explain the basis for the cpDNA diversity observed in many northern taxa. In the arctic, we will assess the importance of refugial survival followed by migration and recent hybridization, while in the Great Plains, we believe widespread species show patterns of high haplotype diversity that may be interpretable in the context of post-glacial migration patterns and resultant hybridization among newly overlapping species. Along the west coast two factors appear important; (i) serpentine soils have shaped the evolution of numerous plant groups including Packera by exerting selection for edaphic tolerance among colonizers and (ii) various coastal refugia may have provided a source of genetic diversity for post-glacial colonizing species throughout this region. Our phylogeographic studies of Packera over the next five years, will improve our understanding of the evolutionary importance of all of these factors and thereby greatly improve our understanding of factors affecting the evolution of the North American flora.