The processes underpinning spatial patterns of genetic diversity are not yet fully understood. Recent years have, however, witnessed an explosion of research using DNA to infer the evolutionary and biogeographic impacts of the Last Glacial Maximum (LGM, around 20,000 years ago). Hundreds of taxa have been found to show relatively high genetic diversity in ‘refugial’ regions unaffected by LGM ice, whereas populations in recolonised areas generally have lower genetic diversity. As an example, many terrestrial taxa have persisted on the Antarctic continent through Pleistocene glaciations, yet LGM ice cover was extreme. To test the hypothesis that Antarctic volcanoes could have nurtured hotspots of refugial diversity through ice ages, I have been combining genomic data with spatial environmental analyses to assess broad-scale diversity patterns. Results indicate that diversity generally declines with distance from geothermal regions, consistent with recent recolonisation of new ice-free terrain from volcanic refugia.
Intriguingly, such molecular signatures of past disturbance events can apparently endure for millennia, despite ongoing dispersal of organisms. This inertia has been suggested to result from early colonists rapidly reaching densities sufficient to block establishment by latecoming conspecific lineages. If these ‘density-blocking’ processes indeed underpin such structure, turnover should depend on subsequent disturbance events that ‘clear the slate’ and allow different lineages to establish. A new research programme will aim to directly test the role of disturbance in structuring spatial genetic patterns, using manipulative experiments as well as opportunities provided by large natural disturbances, e.g., earthquakes (including the November 2016 earthquakes in New Zealand).