17.10.2017: Manuela Dal FORNO (Washington): Lichen Battlefield: Mycobiont versus Photobiont Diversity in Tropical Dictyonema Basidiolichens, HS 32.01, Institut für Pflanzenwissenschaften, Bereich Syst. Botanik und Geobotanik, Holteigasse 6, 17:00 Uhr.
The Dictyonema clade is a large group of lichenized basidiomycetes that have a variety of morphologies, from crustose to foliose thalli, and all with Rhizonema as its cyanobacterial photobiont. These lichens have a unique combination of rare features, since they are basidiolichens (most lichens are Ascomycota) and cyanolichens (lichens mostly have a green algae as photobiont). The distribution of the species is mainly pantropical, with a few found in temperate zones. Whereas many species are now detected as the fungal partner, only 136 species in five genera have been formally recognized with most of the species remaining to be undescribed. However, our knowledge of the cyanobacterial species is far behind, with only one species validly published. To compare the diversity of both symbionts in this symbiotic association, we obtained 16S rDNA bacterial sequences generated through multi-tag pyrosequencing (MTPS) and ITS fungal barcoding generated mainly through Sanger sequencing from 560 specimens representing all major clades within Dictyonema s.l. collected from 19 countries. Regarding the Dictyonema fungi, we found that there are possibly over 300 species, most of them with a narrow geographic range but with distinct morphological, anatomical and ecological characters. Regarding the cyanobacteria Rhizonema, phylogenetic trees and TCS network analyses suggest approximately five species. There is no indication of photobiont-mycobiont co-evolution at the species level in any of the clades of Dictyonema s.l. Nonetheless, one of the lineages of Rhizonema appears to partner primarily with one of the Cora clades found mostly in northern Andean locations. Overall, our results show that the diversity of photobionts is far lower than that of the mycobionts, which supports previously published hypotheses concerning photobiont sharing between fungal species in lichens.