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

点击翻译按钮获取中文摘要

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.