How did macrolichens evolve? The fungal lineages that form lichens began to diversify around the same time that vertebrates moved on to land, 350 to 400 million years ago, and depending on how you count them, 10 to 12 distinct, major lineages survived to the present day. Within each of these can be found an array of lichen symbioses ranging from biofilm-like crusts to architecturally complex macrolichens. The transition from saprobic fungi to lichen associations – symbioses with photosynthetic partners – is one step that required the partners to overcome pathogen and defense mechanisms to develop a stable mutualistic relationship. But further on, what innovations made it possible for lichens to make the jump from thin biofilms to complex, self-replicating architectures? In the Master’s thesis of Kevin Schneider recent published in Molecular Ecology, we found that in trapelioid lichens, a size increase jump was associated with acquisition of nitrogen-fixing cyanobacteria. In a more recent study published in Science, we found that most parmelioid macrolichens contain basidiomycete yeasts in their cortex (above), challenging the paradigm that lichens are constructed by a single fungus. Whether or not these yeasts played a role in the switch to macrolichen architectures is unknown, but by mapping their occurrence we expect to gain insight into correlation and causation of symbiont acquisition in lichens.
Evolution of substrate specificity in lichens. Lichens are famous indicator species and extremely specific about what kinds of substrates they grow on. But what biological mechanism prevents a lichen, presumably self-sufficient with its photosynthesizing alga, from establishing on a substrate it has rained its propagules on? Together with Philipp Resl and colleagues at the University of Graz, I am triangulating on this phenomenon from two angles. First, we are reconstructing how substrate specificity is acquired or lost over a deep phylogenetic tree of more than 180 fungal species; and second, we are mapping metabolic pathways in select genomes from this phylogeny to scan for patterns associated with certain substrate affinities. The project is funded by the Austrian Science Foundation.
Lichen diversity in the southeast Alaska temperate rainforest ecosystem. Some of the highest diversity of lichenized fungi on the planet has been documenting from cool, wet, high latitude climates. I recently wrapped up a three-year project with Alan Fryday of Michigan State University and several other colleagues mapping lichen diversity in Glacier Bay National Park, Alaska (right). Together we documented over 800 species from the Park and 40 new species to science across all major orders of lichenized fungi. Field projects like this are key for communicating the importance of lichens to the public and land managers and acquiring fresh material of rare and phylogenetically isolated species. My previous southeast Alaska project, along the Klondike Gold Rush trails, was covered by the Alaska Public Radio Network. Both projects were funded by the U.S. National Park Service.
Systematics of the wood-inhabiting lichen genus Xylographa. Wood-dependent organisms, often called saproxylic or lignicolous organisms, have been a major focus on conservation in areas with industrial forestry, and many studies have focused on invertebrates and cap fungi. My 2008 review of wood-inhabiting lichens identified big research gaps specific to species diversity on dead wood. After eight years of intermittent study I am pleased that a monograph of the genus Xylographa, completed with colleagues from the Universities of Graz, Helsinki and Bergen, the Spanish National Museum of Natural Sciences and the Field Museum of Chicago, is now finished. Xylographa is one of the most important genera of wood-inhabiting, lichenized fungi in the boreal forest and our species descriptions and keys will pave the way for refined species conservation and substrate use assessments. The completed work also dovetails with an ongoing project I am involved in on substrate specificity in lichens (see below).
Download the monograph here.
Download the monograph here.