Tracing the evolutionary trajectory of allotetraploid StH-genomic Elymus species

长期以来，多倍化一直被认为是植物多样化和物种形成的重要原因。通过杂交的基因流动在物种形成中起着重要作用。更好地了解多倍体的形成过程和每个多倍体物种中基因流动的后果对于研究进化具有广泛的兴趣。冰草属披碱草与小麦、大麦和黑麦同属一类。该属中的牧草适应了不同的气候和生境，使它们成为谷物和饲料育种的宝贵遗传资源，也是进化、分类学和物种形成研究的优秀类群。所有的冰草都是由至少两组不同的染色体组成的，大多数物种都有S染色体和S染色体的组合。与Sth组合的物种约有50种。ST基因组来自假鹅观草属的祖先种，H来自野生大麦。Sth基因组物种分布于从北极到亚热带，从海平面到喜马拉雅5000米以上的地区，其形态非常多样和复杂。鉴于Sth基因组物种的广泛分布和多样化适应，物种形成主要是由于单一起源，然后是差异选择导致适应和分化成多个物种，还是进化历史上在不同时间和地点反复发生的多来源杂交？我们将使用每个物种的几个个体和多组DNA序列数据来解决关于披碱草属Sth物种的多个起源和单一起源的长期争议，并追踪网状事件及其对系统发育关系和物种形成的影响。大多数异源四倍体披碱草物种可以杂交，形成部分或完全可育的杂交种，这导致了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需的遗传分化，但将导致从一个物种到另一个物种的持续基因流动，这将打破先前建立的物种边界。在披碱草属植物中，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检验。我们将调查披碱草物种间的渗透程度及其在物种形成中的作用。种群遗传学方法将被用来分析重叠种群中的标记模式，将它们与非重叠种群进行比较，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。它们还将具有农学相关性，因为披碱草属植物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。

Polyploidization has long been recognized as important causes of plant diversification and speciation. Gene flow through hybridization plays an important role 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. The StH genome species are found from the arctic to the subtropics, from sea level to above 5000m in the Himalayas, and their morphology is very diverse and complex. Given the wide distribution and the diverse adaptation of StH genome species, is speciation mainly due to a single origin followed by differential selection leading to adaptation and differentiation into a number of species, or multiple origins of hybridizations that have happened repeatedly at different times and places during evolutionary history? We will use several individuals per species and multiple sets of DNA sequence data to resolve a long-lasting controversy concerning multiple vs. single origins for StH species of Elymus and to trace reticulate events and their impact on phylogenetic relationships and speciation. 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 investigate the extent of introgression among Elymus species and its role in speciation. Population genetic approaches will be used to analyze the pattern of markers in overlapping populations, comparing them to the non-overlapping 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.