Living in each other’s pockets: insights into the life cycle of Tremella caloplacae s. l.

Complex life-cycles are common among fungi. Dimorphism in basidiomycetes involves alternation between a unicellular yeast phase and a filamentous phase, frequently forming basidiomata. Here we have studied the dimorphic life cycle of the lichen-inhabiting basidiomycetes in the <i>Tremella caloplacae</i> species complex, with particular focus on the newly distinguished <i>Tremella parietinae</i>. Using FISH-CLSM, PCR and Sanger sequencing, we have investigated the presence and distribution of the different life-cycle phases of <i>T. parietinae</i> within the lichen <i>Xanthoria parietina</i>, and also conducted an exploratory investigation into the presence of a <i>Tremella</i> yeast phase in other lichens of the <i>Teloschistaceae</i>. We could show that the filamentous phase of <i>T. parietinae</i> is restricted to the hymenium of <i>X. parietina</i>, whereas the yeast phase also grows elsewhere in the thallus. <i>Tremella caloplacae</i> s. str. is detected by PCR in <i>Calogaya</i>, <i>Flavoplaca</i> and <i>Gyalolechia</i> lichens, whereas its basidiomata are restricted to <i>Variospora</i> lichens. These findings suggests different lichen-specificity of <i>T. caloplacae</i> in the different phases of its life-cycle.