Dissertation Research: Systematics and Evolution of Tarasa (Malvaceae): An Enigmatic Andean Polyploid Genus.

9902230辛普森和泰特蒲公英属(锦葵科)植物的进化受到多倍体(染色体加倍)和安第斯山脉和中美洲山脉地质历史的影响。这30个已知物种分布在从秘鲁中部到智利南部和阿根廷海拔2000-4200米的地方，有两个物种在墨西哥中部的高地分离。塔拉萨的物种要么是二倍体(2n)，具有正常的染色体补充；要么是四倍体(4n)，具有两倍的正常补充。大多数多倍体物种比它们的二倍体物种具有更大的细胞(以及通常更大的整体形态特征)，并且通常是多年生植物而不是一年生植物。然而，塔拉萨属的四倍体物种是不寻常的，因为它们都是一年生植物，与二倍体物种相比，花部特征减少。这个群体的另一个有趣的特征是，四倍体物种都在安第斯山脉比二倍体物种发现的海拔更高。由于其不同寻常的特征，该物种提供了一个独特的机会来研究多倍体、生活史习性和形态之间的相互作用，这些因素导致了墨西哥和南美洲目前不连续的地理分布。研究生詹妮弗·泰特在德克萨斯大学贝丽尔·辛普森博士的指导下，研究了塔拉萨属物种的分类和系统发育关系，以及它们在Sphaeralcea属、Nototriche属和Acaulimalva属的近亲。利用形态和细胞学(染色体)特征，辅以来自核基因和叶绿体基因DNA序列的新分子数据，他们计划重建塔拉萨属物种的系统发育或系谱历史。随着系统发育框架的建立，研究人员可以探索特定的进化和生物地理问题，例如四倍体物种是否来自单一的染色体加倍事件，或者它们是否多次出现，可能来自不同的二倍体物种。同样，他们将能够探索安第斯山脉物种迁徙方向的想法，例如，塔拉萨物种是从智利南部和阿根廷向北迁徙，还是从该山脉最北端的墨西哥地区向南迁徙。系统发育将有助于确定墨西哥的这两个物种是否代表单一的谱系(支系)，或者它们是否独立于不同的物种形成事件而到来。生物地理学的一个中心目标是在不相关的分类学群体中找到类似的模式，为重大历史事件提供指南。然而，基于严格的方法和数据的安第斯植物群的系统发育在数量上很少，因此限制了解释植物分布所需的模型。这项研究将有助于我们加深对安第斯高山植物演化的认识。

9902230Simpson and Tate The evolution of the plant genus Tarasa (Malvaceae) has been influenced by polyploidy (doubling of chromosomes) and by the geological history of the Andean and Central American mountains. The 30 known species are found at elevations between 2000-4200 meters from central Peru to southern Chile and Argentina, and with two species disjunct in the highlands of central Mexico. The species of Tarasa are either diploid (2n) with the normal complement of chromosomes or tetraploid (4n) with twice the normal complement. Most polyploid species have larger cells (and often larger morphological features overall) than their diploid counterparts and are usually perennials rather than annuals. The tetraploid species of Tarasa, however, are unusual in that all are annuals and have reduced floral features as compared to the diploid species. Another interesting feature of this group is that the tetraploid species are all found at higher elevations in the Andes than the diploids. Because of their unusual features, the species present a unique opportunity to study the interactions among polyploidy, life-cycle habit, and morphology that have led to the present disjunct geographic distributions in Mexico and South America.Graduate student Jennifer Tate, under the direction of Dr. Beryl Simpson at the University of Texas, is studying the taxonomic classification and phylogenetic relationships of the species of Tarasa and their close relatives in the genera Sphaeralcea, Nototriche, and Acaulimalva. Using morphological and cytological (chromosomal) characters, supplemented with new molecular data from DNA sequences of nuclear and chloroplast genes, they plan to reconstruct the phylogeny or genealogical history of the species of Tarasa. With a phylogenetic framework in place, the investigators can explore specific evolutionary and biogeographic questions, such as whether the tetraploid species are derived from a single chromosome-doubling event or whether theyhave arisen multiple times, perhaps from different diploid species. Likewise, they will be able to explore ideas about the direction of species migration in the Andes, for example, whether the species of Tarasa moved northward from southern Chile and Argentina or whether they migrated southward from the northernmost Mexican area of the range. The phylogeny will help to determine whether the two species in Mexico represent a single lineage (clade) or whether they arrived independently from separate speciation events. A central goal of biogeography is to find similar patterns in unrelated taxonomic groups that provide a guide to major historical events. However, phylogenies for Andean groups of plants, based on rigorous methods and data, are few in number and hence limit the models necessary for explaining plant distributions. This study will contribute to our developing knowledge of the evolution of high Andean plants.