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

Packera是菊科（雏菊）家族中50多个物种的属，是旨在了解北美植物群进化历史的研究的理想群体，因为（i）它在北美广泛分布，与所有主要生物群落中出现的物种（ii）由于明显的杂交和基因渗入，许多物种的定义不明确，因此杂交模式和由此产生的基因流动都可能是不确定的。在一系列的历史和地理背景下检查和（iii）高水平的种群内叶绿体DNA（cpDNA）单倍型多样性提供了一个来源的分子标记，比可以在系统发育的背景下进行分析。帕克拉起源于墨西哥，并在那里多样化，在大平原，北极和沿着北美西海岸。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，避难所生存和物种迁移在植物群进化中的作用。我们将研究分子分歧的核和cpDNA从两个墨西哥山脉的地方Packera分歧，以确定这是否，其次是北方迁移和广泛的杂交将解释的基础上观察到的cpDNA多样性在许多北方类群。在北极，我们将评估避难生存的重要性，其次是迁移和最近的杂交，而在大平原，我们相信广泛的物种显示模式的高单倍型多样性，可以解释的背景下，冰后期的迁移模式和由此产生的杂交之间的新重叠的物种。沿着西海岸的两个因素显得很重要;（一）蛇纹岩土壤塑造了许多植物群，包括Packera的进化，通过施加选择殖民者之间的土壤耐受性和（ii）各种沿海避难所可能提供了一个来源的遗传多样性的冰川后殖民物种在整个地区。 我们在未来五年内对帕克拉的地理学研究，将提高我们对所有这些因素的进化重要性的理解，从而大大提高我们对影响北美植物群进化的因素的理解。

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.