Tracing the evolutionary trajectory of allotetraploid StH-genomic Elymus species

多倍体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的基因流动的后果是研究进化的广泛兴趣。麦草属与小麦、大麦和黑麦属于同一类群。这一属的禾本科植物已经适应了各种气候和栖息地，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群体。所有的小麦草都由至少两组不同的染色体组成，其中大多数品种都有StY和StH染色体组合。有StH组合的物种约有50种。其中St基因组来自于原属Pseudoroegneria， H基因组来自于野生大麦。从北极到亚热带，从海平面到喜马拉雅山5000m以上，都发现了StH基因组物种，它们的形态非常多样和复杂。考虑到StH基因组物种的广泛分布和多样化适应，物种的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为多个物种，还是在进化史上不同时间和地点反复发生的多重杂交起源？我们将使用每个物种的几个个体和多组DNA序列数据来解决长期以来关于羊草的多个或单一起源的争议，并追踪网状事件及其对系统发育关系和物种形成的影响。大多数异源四倍体羊草物种可以杂交，形成部分或完全可育的杂种，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必需的遗传分化，但会导致基因从一个物种持续流入另一个物种，从而打破先前建立的物种界限。基因流动的程度及其在羊草中创造多样性和物种形成中的作用尚未得到研究。我们将研究羊草种间的渐渗程度及其在物种形成中的作用。种群遗传学方法将用于分析重叠种群中标记的模式，将它们与非重叠种群进行比较，以确定重叠区域和单独区域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结果提供新的见解，并指导保护决策。由于羊草属中有许多农业上有用的物种，它们也将具有农艺学意义。更好地了解过去杂交事件的动态性质也将有助于准确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.