Conquering the Whole World: the Grass Deschampsia cespitosa

Transcontinental or even world-wide distribution of plants is a common phenomenon on the levels of families and genera. There are also several cases of a single species distributed on two or more continents, especially in the northern hemisphere. However, there are very few cases of world-wide distribution of plant species, that do not result from direct or indirect human aided dispersal. The tufted hair grass (Deschampsia cespitosa) occurs in (semi-)natural habitats worldwide in temperate zones (including tropical high mountains) and is thought to have achieved its present day distribution essentially without human assistance. We want to study the pathways and the chronology of long distance dispersal leading to its present world-wide distribution. In detail we want to investigate the biogeographic patterns, i.e. the relationships among the Eurasian, North and South American (including Antarctica), African, and Australasian populations and the evolution of polyploid variants in various regions. Using molecular (chloroplast DNA = cpDNA) and genomic tools (Restriction site Associated DNA markers = RADseq) we aim to identify source populations and their derivates. The cpDNA data are expected to provide a global picture of relationships and dispersal routes within and between geographical regions and continents. Single Nucleotide Polymorphism (SNP) patterns gained from RADseq data will deliver more precise information on divergence among populations within regions and among them. These data will also provide information on genetic structure and diversity, and help in revealing population history, for instance possible phases of very small founder populations following arrival after long-distance dispersal. Cytogenetic tools (Flow CytoMetry = FCM, chromosome counts) will be applied to identify chromosome numbers and ploidy levels. Morphological data will be collected from vouchers and herbaria to gain a global picture of variation in this grass species and a perception on how the morphological variation is related to genetic and genomic patterns. This will help in evaluating the status of the many local variants or subspecies (local endemics). For a European subsample of those local endemics we will collect habitat data in more detail and relate them to the morphological and genetic/genomic data. We think that this first biogeographic study using the combination of above introduced tools in a grass species on a worldwide scale will provide new insights into the history of plant dispersal and the evolution of grassland ecosystems in temperate regions.

We have investigated the biogeography on a worldwide scale in the grass species Deschampsia cespitosa occuring on all continents including several of its presumptive derivates. This grass is one of the rare cases of a worldwide distribution of a single species which has not clearly resulted from modern human dispersal. The grass provides an excellent model taxon to investigate how divergence is related to isolation by distance on several intercontinental, continental, and regional scales and how this can be related to a relative time-scale and patterns of dispersal/migration. We have used Next Generation Sequencing techniques, genome size measurements, and morphometric data for this purpose. Leaf samples were collected mostly in the field together with coarse habitat data and coordinates. Of course this was only possible with the help of several colleagues of Germany, Iceland, Norway, Sweden, Croatia, Spain, Ukraine, Estonia, Russia, China, South Korea, New Zealand, South Africa, USA, Canada and finally of our institute and other colleagues of Austria. However, we had to learn that our plans concerning the worldwide sampling schedule, have turned out to be too optimistic. Several initial consents for help in sampling did not work out properly or with severe delay. Finally, due to restrictions caused by the pandemic we had to modify our original sampling strategy in some regions. Therefore, we could not finish in 2020 as originally scheduled and we have asked FWF for extention until November 2021. Using extractions from herbarium samples helped to cover the respective unsampled regions. Our research provides new insights into the history of polyploids by revealing genetically distant old periglacial relictic tetraploids with partly facultative pseudovivipary bound to special ecology and newly formed seed producing tetraploids without specific habitat requirements showing no divergence from the widespread diploid taxon. Regarding the evolution of endemic Deschampsia-species in New Zealand we found that the endemics on this isolated island are descendents of a late Miocene/Pliocene migration event and connect to another Deschampsia taxon of the southern hemisphere while Deschampsia cespitosa of New Zealand although involved in hybridization with the endemics results from a younger immigration and connects to samples of the northern hemisphere. In Europe we found a complex pattern resulting basically from the climatic history generating a pattern in part similar to those in other organisms, which is, however, blurred by increasing human impact during the Anthropocene. Another manuscript regarding biogeography in Asia is in progress. We are addressing species concepts given the fundamental incongruence between genomic structure and present taxonomy based on often minor morphological variation which has resulted in many regional species especially in Russia. For the final analysis on the global scale (relationships between North America, Eurasia, and the southern hemisphere) we are still analyzing data.