title: Extreme phenotypic variation in Cetraria aculeata (lichenized Ascomycota): adaptation or incidental modification?
abstract: OBJECTIVE
  Phenotypic variability is a successful strategy in lichens for colonizing different habitats. Vagrancy has been reported as a specific adaptation for lichens living in steppe habitats around the world. Among the facultatively vagrant species, the cosmopolitan Cetraria aculeata apparently forms extremely modified vagrant thalli in steppe habitats of Central Spain. The aim of this study was to investigate whether these changes are phenotypic plasticity (a single genotype producing different phenotypes), by characterizing the anatomical and ultrastructural changes observed in vagrant morphs, and measuring differences in ecophysiological performance.
  
  
  METHODS
  Specimens of vagrant and attached populations of C. aculeata were collected on the steppes of Central Spain. The fungal internal transcribed spacer (ITS), glyceraldehyde-3-phosphate dehydrogenase (GPD) and the large sub-unit of the mitochondrial ribosomal DNA (mtLSUm), and the algal ITS and actin were studied within a population genetics framework. Semi-thin and ultrathin sections were analysed by means of optical, scanning electron and transmission electron microscopy. Gas exchange and chlorophyll fluorescence were used to compare the physiological performance of both morphs.
  
  
  CONCLUSIONS
  Vagrant and attached morphs share multilocus haplotypes which may indicate that they belong to the same species in spite of their completely different anatomy. However, differentiation tests suggested that vagrant specimens do not represent a random sub-set of the surrounding population. The morphological differences were related to anatomical and ultrastructural differences. Large intercalary growth rates of thalli after the loss of the basal-apical thallus polarity may be the cause of the increased growth shown by vagrant specimens. The anatomical and morphological changes lead to greater duration of ecophysiological activity in vagrant specimens. Although the anatomical and physiological changes could be chance effects, the genetic differentiation between vagrant and attached sub-populations and the higher biomass of the former show fitness effects and adaptation to dry environmental conditions in steppe habitats.
authors.affiliation: Museo Nacional de Ciencias Naturales, MNCN-CSIC, c/ Serrano 115 dpdo, E-28006 Madrid, Spain. sperezortega@mncn.csic.es
authors.forename: Sergio
authors.initials: S
authors.lastname: Pérez-Ortega
authors.forename: Fernando
authors.initials: F
authors.lastname: Fernández-Mendoza
authors.forename: José
authors.initials: J
authors.lastname: Raggio
authors.forename: Mercedes
authors.initials: M
authors.lastname: Vivas
authors.forename: Carmen
authors.initials: C
authors.lastname: Ascaso
authors.forename: Leopoldo G
authors.initials: LG
authors.lastname: Sancho
authors.forename: Christian
authors.initials: C
authors.lastname: Printzen
authors.forename: Asunción
authors.initials: A
authors.lastname: de Los Ríos
mesh_terms: D000064:Acclimatization; D001203:Ascomycota / Q000166:cytology* / Q000235:genetics*; D002980:Climate; D014644:Genetic Variation; D008011:Lichens / Q000166:cytology* / Q000235:genetics*; D010641:Phenotype; D017422:Sequence Analysis, DNA; D013030:Spain