Evolution of an Allotetraploid Genus: Relationships among North American Species of Elymus (Poaceae:Triticeae)

9974181梅森-Gamer物种形成的过程通常被描述为一个分裂过程，在此过程中，一个物种内的种群彼此分化，最终积累了足够的差异，被归类为单独的物种。然而，当两个不同的谱系走到一起，或形成网状，创造一个杂交谱系时，也可能出现新的物种。这种不同谱系的网状结构似乎在植物中比在动物中更为常见。植物中最常见的杂交机制，多倍体，涉及来自两个亲本的整组基因组（染色体）的相加组合。因此，产生的多倍体杂种比任何一个亲本都有更多的染色体。多倍体在某些植物类群中很少见，但在许多其他类群中却极为常见。例如，在禾本科中，包括爱达荷州大学的梅森-加默博士在这项研究中检查的物种，大约70%的物种似乎是多倍体。此外，多倍性涉及禾本科许多重要作物的起源，包括小麦、燕麦和甘蔗。由于多倍体在许多植物类群中是如此普遍，因此值得加强研究，以阐明多倍体起源和多样化的模式。禾本科植物，小麦族的一个成员，是一个有用的系统，为研究多倍体。首先，它是一个极其广泛和多样化的植物群，因此很好地说明了多倍体物种的进化潜力。其次，其假定的祖先的基因组被很好地表征，特别是在二倍体属Critesion和Pseudoroegneria的北美类群;因此，Escherichus的基因组可能有可识别的起源。通过对北美种的核和叶绿体DNA标记的研究，将进一步加深对几个问题的认识。是否所有北美物种的基因组都有相同或相似的组合？这些结果将有助于建立该属的分类和进化界限。相似的多倍体基因组组合是否出现过不止一次？换句话说，一个物种或属可以有多个起源吗？一个物种可能有多个起源，这一想法给我们关于物种如何起源、持续和多样化的观点增加了另一个层次的复杂性。虽然Escherichus中多倍体的具体特征可能不一定适用于所有植物，但了解塑造这个复杂属的过程将促进植物进化和多样性的知识。

9974181Mason-Gamer The process of speciation is usually characterized as a splitting, during which populations within a species diverge from one another, eventually accumulating enough differences to be classified as separate species. However, new species can also arise when two divergent lineages come together, or reticulate, creating a hybrid lineage. Such reticulation of distinct lineages appears to be far more common in plants than in animals. The most common mechanism of hybridization in plants, polyploidy, involves additive combinations of entire sets of genomes (of chromosomes) from two parents. The resulting polyploid hybrids therefore have more chromosomes than either parent. Polyploidy is rare in some groups of plants, but extremely common in many others. In the grass family Poaceae, for example, which includes the species examined in this research by Dr. Mason-Gamer at the University of Idaho, about 70% of all species appear to be polyploid. Furthermore, polyploidy is involved in the origin of many important crops in the Poaceae, including the wheats, oats, and sugarcane. Because it is so common in many groups of plants, polyploidy deserves increased study to clarify patterns of polyploid origin and diversification. The grass genus Elymus, a member of the wheat tribe Triticeae, serves as a useful system for the study of polyploidy. First, it is an extremely widespread and diverse group of plants, and so illustrates well the evolutionary potential of polyploid species. Second, the genomes of its presumed progenitors are well characterized, particularly for the North American taxa in the diploid genera Critesion and Pseudoroegneria; therefore, the genomes of Elymus are likely to have recognizable origins. Studies of nuclear and chloroplast DNA markers from the North American species of Elymus will further understanding of several questions. Do all North American species of Elymus have the same or similar combinations of genomes? The answers will help to establish the taxonomic and evolutionary boundaries of the genus. Have similar polyploid genome combinations arisen more than once? In other words, can a single species or genus have multiple origins? The idea that one species may have multiple origins adds yet another level of complexity to our views of how species originate, persist, and diversify. While the specific features of polyploidy in Elymus may not necessarily apply to all plants, understanding the processes that have shaped this complex genus will advance knowledge of plant evolution and diversity.