Das Projekt "Genetic diversity and geographical differentiation of green-algal photobionts in Antarctic lichens" wird vom Umweltbundesamt gefördert und von Senckenbergische Naturforschende Gesellschaft, Forschungsinstitut und Naturmuseum Senckenberg durchgeführt. The biomass and diversity of terrestrial Antarctic ecosystems is almost entirely made up of bryophytes and lichens. As highly specialized symbiotic systems of fungi and algae or cyanobacteria lichens are especially sensitive to rapid climatic changes. Lichen fungi depend critically on the availability and ecological performance of suitable algal strains and genotypes in their environment. Up to now, the genetic diversity and geographical differentiation of Antarctic green algal lichen photobionts has not been studied in detail and little is known about the photobiont selectivity of green algal lichens. Based on DNA-sequences, we study the genetic diversity and structure of Antarctic populations of trebouxioid lichen photobionts and mycobionts and compare them with populations from other continents. As a model system, the photobiont diversity in different haplotypes of the macrolichen Cetraria aculeata is examined and compared to the genetic diversity of Cetraria-mycobionts and the total organismal stand diversity. We are especially interested in the question, how strongly Antarctic populations of C. aculeata select for certain photobiont strains and whether Antarctic photobiont populations are genetically isolated from those of other continents. First results indicate reduced levels of genetic diversity in Antarctic mycobiont and photobiont populations. The photobiont of Cetraria aculeata belongs to the Trebouxia jamesii group. With the exception of a few rare haplotypes, there seem to be no specifically Antarctic haplotypes. Most notably, Antarctic photobiont haplotypes are closely related to or even identical with arctic haplotypes, while temperate populations of Cetraria aculeata associate with genetically different photobionts. Although C. aculeata is usually sterile and propagates by thallus fragments that contain both symbionts, the mycobiont displays a different phylogeographic pattern with northern and southern hemispheric haplotypes. This indicates habitat-specific association of mycobionts with photobionts.