Ancient genetic signatures and long distance dispersal in a marine foundation species

Sea levels fluctuate considerably between glacial and interglacial periods. As a result, coastal margins fluctuate between inundation in which intertidal and marine communities establish and exposed dry land where terrestrial... [ view full abstract ]

Sea levels fluctuate considerably between glacial and interglacial periods. As a result, coastal margins fluctuate between inundation in which intertidal and marine communities establish and exposed dry land where terrestrial communities prevail. Significant shoreline changes have occurred along the southern coastlines of Australia. At the peak of the Last Glacial Maximum (LGM), approximately 25,000 years ago, an extensive land bridge connected Tasmania to the Australian mainland. We are interested in the role of the two Australian boundary currents, the East Australian Current (EAC) and the Zeehan Current (ZC), compared to inshore currents and prevailing wind forcing play in shaping population genetic structure for a marine foundation species, Posidonia australis within the Bass Strait following the LGM. We generated multilocus microsatellite DNA genotypes and assessed spatial patterns of genetic diversity and clonality. Overall, there was strong regional spatial genetic structuring among P. australis meadows in southeastern Australia, which was congruent with the three recognized marine biogeographic provinces (Flindersian, Maugean, and Peronian). The Bass Strait meadows show strong signals consistent with: (i) a significant historical genetic break between South Australian meadows, Bass Strait meadows and East Coast meadows; (ii) Wilson’s Promontory not being a barrier to dispersal; (iii) strong similarity between Deal Island and East Coast meadows (Peronian influence via the EAC); (iv) evidence of two zones of admixture; (v) isolation through the LGM and dispersal within Bass Strait, and; (vi) evidence for rare or episodic dispersal (long distance dispersal via the ZC). The data strongly suggest that Bass Strait genotypes survived in isolation from South Australian meadows during the LGM and the location for two refugial populations are hypothesized.