Pleistocene expansion of the bipolar lichen C etraria aculeata into the S outhern hemisphere

Many boreal and polar lichens occupy bipolar distributional ranges that frequently extend into high mountains at lower latitudes. Although such disjunctions are more common among lichens than in other groups of organisms, the geographic origin of bipolar lichen taxa, and the way and time frame in which they colonized their ranges have not been studied in detail. We used the predominantly vegetative, widespread lichen C etraria aculeata as a model species. We surveyed the origin and history of its bipolar pattern using population genetics, phylogenetic and genealogical reconstruction methods. C etraria aculeata originated in the N orthern H emisphere and dispersed southwards during the P leistocene. The genetic signal suggests a P leistocene dispersive burst in which a population size expansion concurred with the acquisition of a S outh‐ A merican range that culminated in the colonization of the A ntarctic.