Evolution of the dry rot fungus Serpula lacrymans and its allies
Appears in the following Collection
- Biologisk institutt 
AbstractThis thesis focuses on the natural history of the dry rot fungus Serpula lacrymans and closely related taxa within Serpulaceae. In the first study the phylogenetic relationships within Serpulaceae have been investigated using multi-locus sequencing. In the resulting phylogeny, two mycorrhiza-forming genera, Austropaxillus and Gymnopaxillus, form a monophyletic group nested within the saprotrophic genus Serpula. This confirms a transition from brown-rot to ectomycorrhizal life style that happened once in a monophyletic Serpulaceae, probably between 60 and 40 million years ago in western North America or, alternatively, in Southern temperate regions after long distance dispersal from North America.
The second study deals with cryptic speciation within the species complex Serpula himantioides which is the sister species to S. lacrymans. Evidence is provided for five cryptic species by four independent gene phylogenies. One of the phylogenetic species shows little phylogeographical structure at a global scale, indicating recent long-distance dispersal. Some of the lineages show adaptation to certain substrates. North and South America appear as the centre of divergence within this morphospecies.
In study III the origin and further worldwide spread of S. lacrymans have been analysed employing different molecular markers. Evidence is provided for that S. lacrymans is divided into two main lineages that probably represent well-differentiated cryptic species; one nonaggressive residing naturally in North America and Asia (var. shastensis), and another aggressive lineage including specimens from all continents, both from natural environments and buildings (var. lacrymans). Mainland Asia is pinpointed as the origin of the aggressive form var. lacrymans, and a few aggressive genotypes have migrated worldwide from Asia to Europe, North and South America and Oceania followed by local population expansions.
The fourth study provides a detailed survey of two major invasive populations of S. lacrymans; one from Japan and one from Europe. Both populations have gone through population bottlenecks prior to local expansion. The European population is extremely genetically depleted leading to the presence of only a few VC types in Europe, while the Japanese population appears to be influenced by higher gene flow from the Asian source population and, correspondingly, more VC types occur in Japan. Clonal dispersal seems very infrequent in both populations.
In study V, global distribution and richness of mating types (MAT A) in S. lacrymans was studied using a mating type linked genetic marker as a proxy. A high allelic richness and molecular variation was detected in the mating type linked marker as compared to other presumably neutral markers. Little geographic variation was observed in this marker as a contrast to other markers investigated earlier. We observed trans-specific polymorphisms as some alleles from the closely related species S. himantioides are more similar to those of S. lacrymans than other alleles from S. himantioides.
Altogether, this thesis illuminates the evolutionary background and the population genetics of the devastating dry rot fungus.
List of papars. Papers I, III and IV are removed from the thesis due to copyright restrictions.
Paper I: Engh IB, Bendiksby M, Carlsen T, Binder M, Kauserud H (2010). Evolutionary history of Serpulacea (Basidiomycota): Molecular phylogeny, historical biogeography and evidence for a single transition of nutritional mode. Manuscript. Not yet published.
Paper II: Carlsen T, Engh IB, DeCock C, Rajchenberg M, Kauserud H (2010). Multiple cryptic species with divergent substrate affinities in the Serpula himantioides species complex. Fungal Biology Volume 115, Issue 1, January 2011, Pages 54-61 doi:10.1016/j.funbio.2010.10.004
Paper III: Kauserud H, Svegården IB, Saetre G-P, Knudsen H, Stensrud Ø, Schmidt O, Doi S, Sugiyama T, Högberg N (2007). Asian origin and rapid global spread of the destructive dry rot fungus Serpula lacrymans. Molecular Ecology, Volume 16, Issue 16, pages, August 2007, Pages 3350–3360, doi:10.1111/j.1365-294X.2007.03387.x
Paper IV: Engh IB, Carlsen T, Saetre G-P, Högberg N, Doi S, Kauserud H (2010). Two invasive populations of the dry rot fungus Serpula lacrymans show divergent population genetic structures. Molecular Ecology, Volume 19, Issue 4, February 2010, pages 706-715. doi:10.1111/j.1365-294X.2009.04505.x
Paper V: Engh IB, Skrede I, Saetre G-P, Kauserud H (2010). High variability in a mating type linked region in the dry rot fungus Serpula lacrymans caused by frequency-dependent selection? BMC Genetics 2010 11:64. Published under a Creative Commons Attribution 2.0 License. doi:10.1186/1471-2156-11-64