Population Genomics of a Rare and a Common Wood-Inhabiting Fungal Species Across Europe

Many species have become threatened during the Anthropocene, requiring conservation strategies based on biological evidence. Wood-inhabiting fungi face multiple threats due to a complex interplay of a short lifespan, removal of dead wood as a resource and climate change. Furthermore, rare fruiting events might restrict dispersal via spores, leading to a significant population genetic structure. Yet, little is known about the genetic structure of both rare and common wood-inhabiting fungal species across Europe. Here, we investigate the rare polypore fungus Antrodiella citrinella, which co-occurs with the common wood-decay fungus Fomitopsis pinicola. We analysed a total of 149 individuals of both species across 13 countries, sequenced their genomes and analysed single-nucleotide polymorphisms. Based on a broad set of analyses, we found a very weak population structure in A. citrinella, suggesting historically wide dispersal and effective gene flow across Europe. In contrast, we found support for two moderately differentiated populations following a southwest-northeast separation in F. pinicola, possibly due to dispersal limitation through its relatively larger spores, a more intense forest use history in southern Europe and a post-glacial history of co-immigration with the main host tree species, Norway spruce. While the weak to moderate genetic structure of wood-inhabiting fungi suggests historically sufficient habitat connectivity, conservation measures should consider strategies providing deadwood as an important habitat to restore and maintain connectivity throughout Europe.