Untangling evolutionary dynamic and speciation of allotetraploid StH-genomic Elymus species by population phylogenetics

杂交和多倍体起源一直被认为是植物多样性和物种形成的重要原因。通过杂交的基因流在物种形成中起着重要的作用。更好地了解多倍体形成过程和基因流在每个多倍体物种的后果是研究进化的广泛兴趣。冰草属Escherichus与小麦、大麦和黑麦属于同一组。本属的禾本科植物适应了不同的气候和生境，使其成为谷物和饲料育种的宝贵遗传资源，也是进化，分类和物种形成研究的优秀群体。所有小麦草都由至少两组不同的染色体组成，大多数物种具有StY和StH染色体组合。约有50个物种具有StH组合。St基因组来自Pseudoroegneria属的祖先物种，H来自野生大麦。根据形态特征，将该属的StH种分为7个组。由于环境和发育阶段都可能影响形态特征，具有相似形态的物种可能在遗传上并不接近。例如，三个欧亚和八个北美的Escherichus分类群的DNA分析并不完全支持形态分类。鉴于遗传因素和环境都可能影响形态特征，我们假设具有相似形态的Escherichus物种之间不一定有遗传关系。大多数多倍体的起源和系统发育尚不清楚，StH多倍体的系统发育研究仍然缺乏基于每个物种的几个个体和多套单拷贝或低拷贝核基因座。因此，我们将使用单拷贝核基因和叶绿体DNA序列分析Escherichus物种，每个物种有4-5个加入沿着与他们的祖先物种。将分析序列数据，以确定这些物种之间的关系;将遗传关系与基于形态学的StH物种拟议部分的界限进行比较，以测试具有相似形态的物种是否彼此遗传相关。了解不完全生殖隔离的物种形成动力学是进化生物学的挑战之一。大多数异源四倍体Escherichus物种可以杂交并形成部分或完全可育的杂种，这导致不同物种之间的基因流动。基因流动可以阻止杂交物种形成所必需的遗传分化，但会导致从一个物种到另一个物种的连续基因流动，这将打破先前建立的物种边界。披碱草属基因流动的程度及其在创造多样性和物种形成中的作用尚未得到研究。我们将使用群体遗传学的方法来调查的程度，渐渗之间的Escherichus物种和其在物种形成的作用。为实现这一目标，本研究利用AFLP、微卫星标记和DNA序列分析技术对20个E. caninus、棘齿真杆菌E. fibrosus、E. mutabilis和E.阿拉斯加，和15个混合种群这些物种。群体遗传学方法将用于分析“混合”群体中的标记模式，并将其与“纯”群体进行比较，以确定重叠区和分离区之间基因流动的可能性。这些研究将为基因渗入和杂交物种形成的基因组和进化后果提供新的见解，并指导保护决策。它们也将具有农学相关性，因为Escherichus中有许多农业上有用的物种。更好地了解过去杂交事件的动态性质也将有助于深入了解准确的分类和生物多样性管理。

Hybridization and polyploidy origin have long been recognized as important causes of plant diversification and speciation. Gene flow through hybridization plays important roles in speciation. A better understanding of polyploidy formation processes and the consequences of gene flow in each polyploid species is of widespread interest for studying evolution. Wheatgrass genus Elymus is within the same group as wheat, barley and rye. Grasses within this genus have adapted to various climates and habitats, making them valuable genetic resources for cereal and forage breeding as well as an excellent group for research in evolution, taxonomy, and speciation. All wheatgrasses are made up of at least two different sets of chromosomes with most species having the StY and StH chromosome combination. There are about 50 species with StH combination. The St genome comes from ancestor species in genus Pseudoroegneria and H from wild barley. Based on morphological traits, the StH species in the genus Elymus were classified into seven sections. Since both environment and the stage of development could affect morphological traits, species with similar morphology may not be close genetically. For example, DNA analysis of three Eurasian and eight North American Elymus taxa did not fully support the morphological classification. Given that both genetic factors and environment could affect morphological traits, we hypothesized that the species in Elymus with similar morphology are not necessarily genetically related to each other. The origin and phylogeny of most polyploids remains unclear, a phylogenetic study of StH polyploids based on several individuals per species and multiple sets of single- or low copy nuclear locus is still lacking. Thus, we will use single copy nuclear gene and chloroplast DNA sequences to analyze Elymus species, each with 4-5 accessions along with their ancestor species. Sequence data will be analyzed to determine relationships among these species; the genetic relationships will be compared with the circumscription of the sections proposed for StH species based on morphology to test whether species with similar morphology are genetically related to each other. Understanding the dynamics of speciation with incomplete reproductive isolation is one of the challenges in evolutionary biology. Most allotetraploid Elymus species can hybridize and form partially or fully fertile hybrids, which causes gene flow between different species. Gene flow can prevent genetic differentiation necessary for hybrid speciation, but will result in continuous gene flow from one species into the other that will break the previously established species boundaries. The extent of gene flow and its role in creating diversity and speciation in Elymus has not been examined. We will use a population genetic approach to investigate the extent of introgression among Elymus species and its role in speciation. To fulfill this, AFLP, microsatellites and DNA sequence will be used to analyze 20 pure populations from E. caninus, E. fibrosus, E. mutabilis and E. alaskanus, and 15 mixed populations of these species. Population genetic approach will be used to analyze the pattern of markers in “mixed” populations, and compare them to the “pure” populations to determine how likely gene flow between overlap zones and separate zones is. These studies will provide new insight into the genomic and evolutionary consequences of introgression and hybridization speciation and guide conservation decisions. They will also have agronomic relevance because of the many agriculturally useful species in Elymus. A better understanding of the dynamic nature of past hybridization events will also lend insight into accurate classification and biodiversity management.