Microclimatic differentiation of gene pools in the Lobaria pulmonaria symbiosis in a primeval forest landscape

Population genetics of the tree-colonizing lichen Lobaria pulmonaria were studied in the largest primeval beech forest of Europe, covering 10 000 ha. During an intensive survey of the area, we collected 1522 thallus fragments originating from 483 trees, which were genotyped with 8 myco- and 14 photobiont-specific microsatellite markers. The mycobiont and photobiont of L. pulmonaria were found to consist of two distinct gene pools, which are co-existing within small areas of 3–180 ha in a homogeneous beech forest. The small-scale distribution pattern of the symbiotic gene pools was linked to altitude, and show habitat partitioning of lineages associated with either floodplains or mountain forests. Using Approximate Bayesian Computation (ABC), we dated the divergence of the two fungal gene pools of L. pulmonaria as the Early Pleistocene. Both fungal gene pools survived the Pleistocene glacial cycles in the Carpathians, though possibly in climatically different refugia. Fungal diversificat...