Format: ORAL

Eva Troner 1*, Robert Lcking2, Julien Bachelier 1

1Institute of Biology/Dahlem Centre of Plant Sciences, Freie Universität Berlin, Altensteinstrasse 6, 14195 Berlin, Germany 2Botanical Garden BO, Freie Universität Berlin, Königin-Luise-Strasse 6-8, 14195 Berlin, Germany

Relationships between the symbionts within the lichen thallus have been studied extensively, but it is still unclear whether their associations, which are usually specific, are driven by the myco- or photobiont and/or aspects of the thallus structure. Here, we examine the nature of mycobiont-photobiont associations in two lichen fungi clades, one in the Ascomycota (Coccocarpia) and one in the Basidiomycota (Dictyonemateae), the latter encompassing the genera Cyphellostereum, Dictyonema, and Cora, which form diverse thalli but are all associating with cyanobacterial photobionts of the same genus, Rhizonema. Using microtome sections, light, fluorescence, and scanning electron microscopy, we confirmed the absence of haustorial association in the ascolichen (Coccocarpia) and the presence of tubular haustoria in Cora, Dictyonema, and Cyphellostereum. Based on our results, we conclude that formation of penetrative haustoria in Rhizonema associations is mycobiont- rather than photobiont-driven and does not correlate with the evolution of a more complex thallus structure in, e.g., Coccocarpia or Cora. We hypothesize that the absence of haustoria in Coccocarpia may be explained by the much older evolutionary age of Coccocarpia (Early Cretaceous vs. Oligocene/Miocene in Dictyonemateae), potentially allowing more time to evolve less intrusive non-haustorial photobiont associations in that lineage over time. We also show that the associations within Dictyonemateae lichens appear histologically quite diverse when compared to one another, especially the presence of carbohydrate secretions around the intrahaustorial hyphae, but conclude that they likely evolved in their most recent common ancestor and may be a new apomorphy for the clade.