Evolutionary Processes Shaping Postglacial Gene Pools of High-Altitude Forests: Evidence from the Endemic Eucalypts of Tasmania

Climatic changes during the Pleistocene were responsible for dramatic redistributions of plant species worldwide. On rugged southern hemisphere island Tasmania, temperature increases following last glaciation saw upslope migration climatically suitable from lowland refugia and expansion eucalypt-dominated forests woodlands in Central Highlands. We integrate multiple lines evidence (chloroplast nuclear DNA markers, seedling morphology, survival common garden experiments) a group closely related endemic eucalypts (the alpine white gums) to argue that (i) Highlands colonised by glacial with hybridisation among previously separated populations, (ii) natural selection has filtered admixed resulting local adaptation harsh sub-alpine environment. Chloroplast haplotype diversity decreased microsatellite increased altitude, chloroplast sharing taxa was common, differentiation morphologically distinct lower compared regions. Local highlands signalled glasshouse trial which directional (QST > FST) had shaped morphological trait variation population differences 35-year-old reciprocal plantings along major environmental gradients. conclude evolutionary response these trees past climate change involved interplay both selection, highlighting importance maintaining interactions under future change.