Advertisement

Vertical and horizontal photobiont transmission within populations of a lichen symbiosis

Authors

  • F. DAL GRANDE,

    1. Biodiversity and Conservation Biology, WSL Swiss Federal Research Institute, 8903 Birmensdorf, Switzerland
    Search for more papers by this author
    • Present Address: Biodiversity and Climate Research Centre (BiK-F), Senckenberg Gesellschaft fuer Naturforschung, 60325 Frankfurt am Main, Germany.

    • These two authors contributed equally to this work and are considered joint first authors.

  • I. WIDMER,

    1. Biodiversity and Conservation Biology, WSL Swiss Federal Research Institute, 8903 Birmensdorf, Switzerland
    Search for more papers by this author
    • Present Address: LPED – Laboratory of Population Environment Development, University of Provence, 13331 Marseille Cedex 03, France.

    • These two authors contributed equally to this work and are considered joint first authors.

  • H.H. WAGNER,

    1. Department of Ecology and Evolutionary Biology, University of Toronto, L5L 1C6 Mississauga, Canada
    Search for more papers by this author
  • C. SCHEIDEGGER

    1. Biodiversity and Conservation Biology, WSL Swiss Federal Research Institute, 8903 Birmensdorf, Switzerland
    Search for more papers by this author

Francesco Dal Grande, Fax: +49 (0)69 798 24771; E-mail: francesco.dalgrande@senckenberg.de, francesco.dalgrande@wsl.ch

Abstract

Lichens are widespread symbioses and play important roles in many terrestrial ecosystems. The genetic structure of lichens is the result of the association between fungal and algal populations constituting the lichen thallus. Using eight fungus- and seven alga-specific highly variable microsatellite markers on within-population spatial genetic data from 62 replicate populations across Europe, North America, Asia and Africa, we investigated the contributions of vertical and horizontal transmission of the photobiont to the genetic structure of the epiphytic lichen Lobaria pulmonaria. Based on pairwise comparisons of multilocus genotypes defined separately for the mycobiont and for the photobiont, we inferred the transmission mode of the photobiont and the relative contribution of somatic mutation and recombination. After constraining the analysis of one symbiont to pairs of individuals with genetically identical symbiotic partners, we found that 77% of fungal and 70% of algal pairs were represented by clones. Thus, the predominant dispersal mode was by means of symbiotic vegetative propagules (vertical transmission), which dispersed fungal and algal clones co-dependently over a short distance, thus shaping the spatial genetic structure up to distances of 20 m. Evidence for somatic mutation generating genetic diversity was found in both symbionts, accounting for 30% of pairwise comparisons in the alga and 15% in the fungus. While the alga did not show statistically significant evidence of recombination, recombination accounted for 7.7% of fungal pairs with identical algae. This implies that, even in a mostly vegetatively reproducing species, horizontal transmission plays a role in shaping the symbiotic association, as shown in many coral and other symbioses in nature.

Ancillary