Speciation mechanisms underlying rapid radiations in South American and Central Asian species of Hordeum (Poaceae)

大麦属(Poaceae)大麦有32种，分布于世界温带地区。对这些分类群的系统发育分析表明，在一个由28个种组成的单系亚群中，有一种快速而相对较新的辐射。很大一部分辐射物种出现在沿海和内陆生境受盐分影响的土壤上。因此，获得耐盐性可能是在这些生境中定居和辐射的一个可能的触发因素。在拟议的项目中，我们想调查关于大麦快速物种形成的两个可能的假设。它们是：(1)耐盐性是一项“关键创新”，允许受盐分影响的生境入侵并促进生态分化，以绕过种下竞争(适应性)；(2)快速辐射是由于远距离扩散(非适应性)后偏远生境中的异地物种形成造成的。为了研究这些假说，我们将启动一项来自辐射支系的四个物种的比较研究，以及这一组的单个姐妹分类单元。我们打算利用核微卫星标记和叶绿体单倍型分析来分析种群结构、基因流动和系统地理。此外，利用基因芯片的基因表达研究，以及受控温室条件下的栽培实验，将被用来深入了解被研究物种之间耐盐性遗传背景的可能差异。这些数据将得到物种自然林分的生态数据的补充，以揭示共生物种对之间生态偏好(生态位)的差异。

The barley genus Hordeum (Poaceae) occurs with 32 species in temperate regions of the world. Phylogenetic analysis of the taxa revealed a rapid and relatively recent radiation within a monophyletic subgroup, comprising 28 of the species. A large fraction of the radiated species occurs on salt influenced soils in coastal and interior habitats. The acquirement of salt tolerance thus could have been a possible trigger for the colonization of and radiation in these habitats. In the proposed project, we like to investigate two possible hypotheses concerning rapid speciation in Hordeum. These are: (1) Salt tolerance is a "key innovation" that allowed the invasion of salt influenced habitats and promoted ecological differentiation to circumvent infraspecific competition (adaptive); (2) rapid radiation is caused by allopatric speciation in remote habitats after long distance dispersal (non-adaptive). To investigate these hypotheses we will initiate a comparative study on four species from the radiated clade, together with the single sistertaxon of this group. We intend to analyze the population structure, the gene flow, and the phylogeography with nuclear microsatellite markers and chloroplast haplotype analysis. Additionally, gene expression studies with cDNA arrays, together with cultivation experiments under controlled greenhouse conditions will be used to get insights in possible differences in the genetic background of salt tolerance among the species under study. These data will be supplemented by ecological data from natural stands of the species to reveal differences in ecological preferences (niches) between sympatrically occurring species pairs.