GLACIAL SURVIVAL DOES NOT MATTER - RAPD PHYLOGEOGRAPHY OF NORDIC SAXIFRAGA OPPOSITIFOLIA

The arctic-alpine Saxifraga oppositifolia has recently been suggested to have survived the last glaciation in high-arctic refugia, based on a finding of more genetic (RFLP) variation in Svalbard compared with m ore southern areas. To elucidate the migration history of this allogam ous species, we analysed 18 populations from Norway, Svalbard and Nova ya Zemlya using random amplified polymorphic DNAs (RAPDs). There was n o more RAPD variation in the high Arctic than further south. In an ana lysis of molecular variance (AMOVA), most of the RAPD variation was fo und within populations (64%). There was less intrapopulational variati on in Svalbard (65%) than in northern Norway (78%) and southern Norway (86%), suggesting that-there is more inbreeding towards the north, pr obably because of lower pollinator activity. Twenty-eight per cent of the RAPD variation was found among populations within these geographic al regions, and only 9% was found among the regions. In PCO and UPGMA analyses, plants and populations of different geographical origins wer e to a large extent intermingled. There was, however, a distinct, sout h-north clinal geographical structuring of the RAPD variation both in the PCO analysis and in a spatial autocorrelation (Mantel) analysis. T hese results suggest that there has been extensive gene flow among mor e or less continuously distributed populations of S. oppositifolia dur ing the Weichselian, and that the extant Nordic populations were estab lished after massive, centripetal immigration from these genetically v ariable, periglacial populations. The postglacial period may not have been sufficiently long for the subsequently isolated populations of th is long-lived, allogamous perennial to diverge. Given the high levels of migration inferred from this study, genetic differentiation of glac ial survivor populations, if any existed, would most likely have been swamped in the postglacial period. Thus, our molecular data support re cent conclusions based on palaeobotanical and biogeographical data tha t the glacial survival hypothesis is superfluous.