title: Intercontinental divergence in the Populus-associated ectomycorrhizal fungus, Tricholoma populinum.
abstract: The ectomycorrhizal fungus Tricholoma populinum is host-specific with Populus species. T. populinum has wind-dispersed progagules and may be capable of long-distance dispersal. In this study, we tested the hypothesis of a panmictic population between Scandinavia and North America. DNA sequences from five nuclear loci were used to assess phylogeographic structure and nucleotide divergence between continents. Tricholoma populinum was composed of Scandinavian and North American lineages with complete absence of shared haplotypes and only one shared nucleotide mutation. Divergence of these lineages was estimated at approx. 1.7-1.0 million yr ago (Ma), which occurred after the estimated divergence of host species Populus tremula and Populus balsamifera/Populus trichocarpa at 5 Ma. Phylogeographic structure was not observed within Scandinavian or North American lineages of T. populinum. Intercontinental divergence appears to have resulted from either allopatric isolation; a recent, rare long-distance dispersal founding event followed by genetic drift; or the response in an obligate mycorrhizal fungus with a narrow host range to contractions and expansion of host distribution during glacial and interglacial episodes within continents. Understanding present genetic variation in populations is important for predicting how obligate symbiotic fungi will adapt to present and future changing climatic conditions.
authors.affiliation: Institute of Arctic Biology, 902 N. Koyukuk Drive, 311 Irving 1 Building, University of Alaska Fairbanks, Fairbanks, AK 99775-7000, USA.|Present address: Biology Program, Centre College, Danville, KY 40422, USA.
authors.forename: Lisa C
authors.initials: LC
authors.lastname: Grubisha
authors.affiliation: Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409, USA.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Levsen
authors.affiliation: Institute of Arctic Biology, 902 N. Koyukuk Drive, 311 Irving 1 Building, University of Alaska Fairbanks, Fairbanks, AK 99775-7000, USA.|Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409, USA.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Olson
authors.affiliation: Institute of Arctic Biology, 902 N. Koyukuk Drive, 311 Irving 1 Building, University of Alaska Fairbanks, Fairbanks, AK 99775-7000, USA.
authors.forename: D
authors.initials: D
authors.lastname: Lee Taylor
mesh_terms: D001499:Bayes Theorem; D014644:Genetic Variation; D005843:Geography; D006239:Haplotypes / Q000235:genetics; D054884:Host-Pathogen Interactions / Q000235:genetics; D008969:Molecular Sequence Data; D038821:Mycorrhizae / Q000235:genetics* / Q000302:isolation & purification; D009656:North America; D009711:Nucleotides / Q000235:genetics; D010802:Phylogeny; D011110:Polymorphism, Genetic; D032107:Populus / Q000382:microbiology*; D012537:Scandinavian and Nordic Countries; D013997:Time Factors; D055439:Tricholoma / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D009711:Nucleotides