Molecular clock evidence for survival of A ntarctic cyanobacteria ( O scillatoriales , P hormidium autumnale ) from P aleozoic times

Cyanobacteria are well adapted to freezing and desiccation; they have been proposed as possible survivors of comprehensive A ntarctic glaciations. Filamentous types from the order O scillatoriales , especially the species P hormidium autumnale K ützing ex G omont 1892, have widely diverse morphotypes that dominate in A ntarctic aquatic microbial mats, seepages, and wet soils. Currently little is known about the dispersion of cyanobacteria in A ntarctica and of their population history. We tested the hypothesis that cyanobacteria survived A ntarctic glaciations directly on site after the G ondwana breakup by using the relaxed and strict molecular clock in the analysis of the 16 S r RNA gene. We estimated that the biogeographic history of A ntarctic cyanobacteria belonging to P . autumnale lineages has ancient origins. The oldest go further back in time than the breakup of G ondwana and originated somewhere on the supercontinent between 442 and 297 Ma. Enhanced speciation rate was found around the time of the opening of the D rake Passage ( c . 31–45 Ma) with beginning of glaciations ( c . 43 Ma). Our results, based primarily on the strains collected in maritime A ntarctica, mostly around J ames R oss I sland, support the hypothesis that long‐term survival took place in glacial refuges. The high morphological diversification of P . autumnale suggested the coevolution of lineages and formation of complex associations with different morphologies, resulting in a specific endemic A ntarctic cyanobacterial flora.