Phylogeographical breaks and limited connectivity among multiple refugia in a pan‐Antarctic moss species.

Aim: The historical biogeography of the Antarctic terrestrial flora remains poorly studied and understood. Long‐term in situ persistence of mosses was demonstrated but region‐wide phylogeographical patterns and processes which shaped extant ranges remain largely unknown. Based on a circum‐Antarctic phylogeography, we aim to explore the location of glacial refugia, especially the possibility of their existence in the continent, patterns of possible connections between extant discrete populations, local colonisation routes and barriers to gene flow, hence relative importance of connectivity and isolation. Location: Antarctica, South America, Australia and New Zealand. Taxon: Syntrichia sarconeurum Ochyra & R.H.Zander (Pottiaceae). Methods: We used a range‐wide, taxonomically informed sampling and multilocus sequencing of nuclear and chloroplast DNA regions. The temporal evolutionary framework, spatial genetic structure and regional diversification were assessed using phylogenetic reconstruction (maximum likelihood and Bayesian inference), molecular dating, phylogeographical analyses and reconstruction of ancestral areas. Results: We found a striking genetic structure of the Antarctic Syntrichia sarconeurum populations that deviates from previous reports on mosses. The presence of two allopatric cpDNA haplotypes indicated a long‐term isolation of the continental populations. Nuclear ITS revealed three major lineages with a main genetic break largely consistent with plastid data. Significant phylogeographical structure was further supported by NST/FST comparison, raggedness index and mismatch analyses. Diversification of the Antarctic lineages occurred within the Pleistocene, since about 1.36 Ma. Main Conclusions: The genetic break genetic break revealed in the phylogeographical structure coincides with the Gressit line, a biogeographical separation area between the biota of the Antarctic Peninsula and the main continental Antarctica. It indicates limited connectivity of populations and suggests that S. sarconeurum has survived in multiple refugia both in the peripheral areas of the Antarctic and within the continent over several glacial periods. Differences in genetic diversity observed between these areas may hypothetically reflect asymmetric changes in reproductive mode in the past. [ABSTRACT FROM AUTHOR]