Surviving climate changes: high genetic diversity and transoceanic gene flow in two arctic-alpine lichens, Flavocetraria cucullata and F-nivalis (Parmeliaceae, Ascomycota)

Aim We examined genetic structure and long-distance gene flow in two lichenized ascomycetes, Flavocetraria cucullata and Flavocetraria nivalis, which are widespread in arctic and alpine tundra. Location Circumpolar North. Methods DNA sequences were obtained for 90 specimens (49 for F. cucullata and 41 for F. nivalis) collected from various locations in Europe, Asia and North America. Sequences of the nuclear internal transcribed spacer (ITS) + 5.8S ribosomal subunit gene region were generated for 89 samples, and supplemented by beta-tubulin (BTUB) and translation elongation factor 1-alpha gene (EF1) sequences for a subset of F. cucullata specimens. Phylogenetic, nonparametric permutation methods and coalescent analyses were used to assess population divergence and to estimate the extent and direction of migration among continents. Results Both F. cucullata and F. nivalis were monophyletic, supporting their morphology-based delimitation, and had high and moderately high intraspecific genetic diversity, respectively. Clades within each species contained specimens from both North America and Eurasia. We found only weak genetic differentiation among North American and Eurasian populations, and evidence for moderate to high transoceanic gene flow. Main conclusions Our results suggest that both F. cucullata and F. nivalis have been able to migrate over large distances in response to climatic fluctuations. The high genetic diversity observed in the Arctic indicates long-term survival at high latitudes, whereas the estimated migration rates and weak geographic population structure suggest a continuing long-distance gene flow between continents that has prevented pronounced genetic differentiation. The mode of long-distance dispersal is unknown, but wind dispersal of conidia and/or ascospores is probably important in the open arctic landscapes. The high genetic diversity and efficient long-distance dispersal capability of F. cucullata and F. nivalis suggest that these species, and perhaps other arctic lichens as well, will be able to track their potential niche in the changing Arctic.