Landscape-level gene flow in Lobaria pulmonaria, an epiphytic lichen.

Epiphytes are strongly affected by the population dynamics of their host trees. Owing to the spatio-temporal dynamics of host tree populations, substantial dispersal rates--corresponding to high levels of gene flow--are needed for populations to persist in a landscape. However, several epiphytic lichens have been suggested to be dispersal-limited, which leads to the expectation of low gene flow at the landscape scale. Here, we study landscape-level genetic structure and gene flow of a putatively dispersal-limited epiphytic lichen, Lobaria pulmonaria. The genetic structure of L. pulmonaria was quantified at three hierarchical levels, based on 923 thalli collected from 41 plots situated within a pasture-woodland landscape and genotyped at six fungal microsatellite loci. We found significant isolation by distance, and significant genetic differentiation both among sampling plots and among trees. Landscape configuration, i.e. the effect of a large open area separating two forested regions, did not leave a traceable pattern in genetic structure, as assessed with partial Mantel tests and analysis of molecular variance. Gene pools were spatially intermingled in the pasture-woodland landscape, as determined by Bayesian analysis of population structure. Evidence for local gene flow was found in a disturbed area that was mainly colonized from nearby sources. Our analyses indicated high rates of gene flow of L. pulmonaria among forest patches, which may reflect the historical connectedness of the landscape through gene movement. These results support the conclusion that dispersal in L. pulmonaria is rather effective, but not spatially unrestricted.