title: Photobiont selectivity leads to ecological tolerance and evolutionary divergence in a polymorphic complex of lichenized fungi.
abstract: OBJECTIVE
  The integrity and evolution of lichen symbioses depend on a fine-tuned combination of algal and fungal genotypes. Geographically widespread species complexes of lichenized fungi can occur in habitats with slightly varying ecological conditions, and it remains unclear how this variation correlates with symbiont selectivity patterns in lichens. In an attempt to address this question, >300 samples were taken of the globally distributed and ecologically variable lichen-forming species complex Tephromela atra, together with closely allied species, in order to study genetic diversity and the selectivity patterns of their photobionts.
  
  
  METHODS
  Lichen thalli of T. atra and of closely related species T. grumosa, T. nashii and T. atrocaesia were collected from six continents, across 24 countries and 62 localities representing a wide range of habitats. Analyses of genetic diversity and phylogenetic relationships were carried out both for photobionts amplified directly from the lichen thalli and from those isolated in axenic cultures. Morphological and anatomical traits were studied with light and transmission electron microscopy in the isolated algal strains.
  
  
  RESULTS
  Tephromela fungal species were found to associate with 12 lineages of Trebouxia. Five new clades demonstrate the still-unrecognized genetic diversity of lichen algae. Culturable, undescribed lineages were also characterized by phenotypic traits. Strong selectivity of the mycobionts for the photobionts was observed in six monophyletic Tephromela clades. Seven Trebouxia lineages were detected in the poorly resolved lineage T. atra sensu lato, where co-occurrence of multiple photobiont lineages in single thalli was repeatedly observed.
  
  
  CONCLUSIONS
  Low selectivity apparently allows widespread lichen-forming fungi to establish successful symbioses with locally adapted photobionts in a broader range of habitats. This flexibility might correlate with both lower phylogenetic resolution and evolutionary divergence in species complexes of crustose lichen-forming fungi.
authors.affiliation: Department of Life Science, University of Trieste, Via Giorgieri 10, 34127 Trieste, Italy Institute of Plant Sciences, Karl-Franzens-University Graz, Holteigasse 6, 8010 Graz, Austria lmuggia@units.it lucia.muggia@uni-graz.at lucia_muggia@hotmail.com.
authors.forename: Lucia
authors.initials: L
authors.lastname: Muggia
authors.affiliation: Departamento de Biología Ambiental, Museo Nacional de Ciencias Naturales (CSIC), C/Serrano 115-dpdo, Madrid, Spain.
authors.forename: Sergio
authors.initials: S
authors.lastname: Pérez-Ortega
authors.affiliation: Institute of Plant Sciences, Karl-Franzens-University Graz, Holteigasse 6, 8010 Graz, Austria.
authors.forename: Theodora
authors.initials: T
authors.lastname: Kopun
authors.affiliation: Institute of Plant Sciences, Karl-Franzens-University Graz, Holteigasse 6, 8010 Graz, Austria.
authors.forename: Günther
authors.initials: G
authors.lastname: Zellnig
authors.affiliation: Institute of Plant Sciences, Karl-Franzens-University Graz, Holteigasse 6, 8010 Graz, Austria.
authors.forename: Martin
authors.initials: M
authors.lastname: Grube
mesh_terms: D020418:Algal Proteins / Q000235:genetics; D001203:Ascomycota / Q000502:physiology; D005075:Biological Evolution; D000460:Chlorophyta / Q000235:genetics* / Q000502:physiology; D048028:DNA, Algal / Q000235:genetics; D021901:DNA, Intergenic / Q000235:genetics; D017753:Ecosystem; D008969:Molecular Sequence Data; D010802:Phylogeny; D018807:Polymorphism, Single-Stranded Conformational; D017422:Sequence Analysis, DNA; D013559:Symbiosis
chemical_list: D020418:Algal Proteins; D048028:DNA, Algal; D021901:DNA, Intergenic
keywords: Adaptation; Lecanoromycetes; Tephromela atra; Trebouxia; algal culture; crustose lichen; lichenized fungi; morphology; mycobiont; photobiont; phylogeny
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