Ecological transitions and evolutionary genomics of the invasive brown rot fungus Serpula lacrymans

This thesis explores the ecological transitions and evolutionary genomics of the dry rot fungus Serpula lacrymans and related species within the Serpulaceae family. Phylogenetics, evolutionary genomic approaches, as well as experimental analyses of wood decay and competition abilities, were used to better understand how Serpula lacrymans has transitioned from living in nature to the built environment. First, the number of genetic markers required to identify cryptic species in Serpula was examined, which revealed that a few, phylogenetically informative DNA markers, can provide a solid demarcation of cryptic species. Then, the ecological adaptations that the destructive house-invading fungus Serpula lacrymans var. lacrymans has gone through in order to colonize woody substrates inside the built environment were examined. Comparative genome analyses showed that var. lacrymans displayed very effective wood decay, while its wild relative, Serpula himantioides showed better competitor abilities. The analysis indicated that var. lacrymans is an ecological specialist with poor competitive ability against other fungi. The study also analyzed the evolution of the wood decay machinery in various Serpula lineages in relation to colonizing various substrates, i.e. its niche breadth. The analysis confirmed that var. lacrymans is more specialized for the rapid decay of specific substrates (spruce), while Serpula himantioides seems to be more of a generalist. The specialist var. lacrymans might be less dependent on nitrogen-intensive enzymatic degradation compared to the more generalist relative Serpula himantioides.