Population biology of foliicolous lichen species

The community structures of selected foliicolous lichens in a tropical lowland rainforest will be investigated by demographic and phytosociological approaches. These will be accompanied by molecular analyses to study population structures and reproductive modes. The community structure will be estimated by inventories of lichens naturally occurring on leaves collected from selected sites, and from lichens that colonise artificial leaves installed in these same sites. Artificial surfaces are rapidly colonised by foliicolous lichens, allowing a study of their establishment and development in situ. All morphological species will be initially identified by phenotype-based keys. The four most abundantly occurring and experimentally tractable lichens will be further characterised by multiple sequence-based DNA loci to delimit the species in a phylogenetic context and to assess genetic variation by comparison with closely related species. Of these phylogenetic species, two that are found to most abundantly colonise artificial leaves will be chosen for further characterization of their population structures and colonization strategies. These analyses will quantify the numbers and spatial distribution of genotypes of a phylogenetic species present in a rainforest plot. This project contributes to the knowledge about the ecology and infraspecific diversity of tropical fungi.

This project investigated the community structure, population genetics, and colonization strategies of foliicolous lichens in a tropical rainforest. We focused on a particularly common genus in these habitats, Porina, and analysed data from several species that co-occur on leaves. To assess the relationships among the species of Porina and a possible coevolution with the associated photobionts, we produced a phylogenetic hypothesis for foliicolous members of this fungal genus. The results of this analysis show that there is no apparent symbiont coevolution in Porina species which propagate with spores, whereas clear correlation of genotypes was found in a species that propagates both symbionts jointly. A strict selectivity for algal strains with similar growth habit was apparent. The genetic diversity within species of lichen fungi varied, and we have evidence that more, genetically different, species exist than are presently recognized by phenotypic methods. Dominating genotypes indicate for rapid colonization by particular adapted strains of some species, and that this is presumably dominating at a narrow local scale. Artificial surfaces were colonized within months by minute thalli and their composition largely depends on the presence of suitable photobionts, whose growth depends on small differences on the surface humidity. Competition for space on leafs seems rather high as the mycobionts rapidly form a wide-spreading mycelium that samples suitable algal symbionts. Similar patterns were also found for species of other genera using epifluorescence microscopic analyses. As a side product we have also investigated the phylogeny of Porina, and found that the family Porinaceae evolved its special morphology (closed conical fruitbodies) within a larger group of ascomycetes with different morphology (open disc-like fruibodies), probably as a neotenic process. A further side product is a first analysis of epiphyllous algae of the order Trentepohliales, which shows unexpected genetic diversity.