Genetic variation within and among populations of the threatened lichen Lobaria pulmonaria in Switzerland and implications for its conservation

The foliose epiphytic lichen Lobaria pulmonaria has suffered a significant decline in European lowlands during the last decades and therefore is consi dered as endangered throughout Europe. An assessment of the genetic variabi lity is necessary to formulate biologically sound conservation recommendati ons for this species. We investigated the genetic diversity of the fungal s ymbiont of L. pulmonaria using 143 specimens sampled from six populations ( two small, one medium, three large) in the lowland, the Jura Mountains, the pre-Alps and the Alps of Switzerland. Among all nuclear and mitochondrial regions sequenced for this study, variability was found only in the interna l transcribed spacer (ITS I), with three polymorphic sites, and in the nucl ear ribosomal large subunit (nrLSU), with four polymorphic sites. The varia ble sites in the nrLSU are all located within a putative spliceosomal intro n. We sequenced these two regions for 81 specimens and detected six genotyp es. Two genotypes were common, two were found only in the more diverse popu lations and two were found only in one population each. There was no correl ation between population size and genetic diversity. The highest genetic di versity was found in populations where the fungal symbiont is reproducing s exually Populations with low genetic diversity included only the two same c ommon genotypes. Our study provides evidence suggesting that L. pulmonaria is self-incompatible and heterothallic. Based on our results we give popula tions with sexually reproducing individuals a higher rank in terms of conse rvation priority than strictly asexual populations. The remaining lowland p opulations are so small, that one single catastrophic event such as a windt hrow might destroy the entire population. Hence we suggest augmenting such populations in size and genetic diversity using small thallus fragments or vegetative diaspores collected in other populations. As we did not detect a ny locally adapted genotypes, these transplants can be taken from any other genetically diverse population in Switzerland.