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The strawberry tree (Arbutus unedo L.) is a native species, water stress and low fertility soils tolerant, actively resistant to wildfires and widely distributed in Portugal. The fruit is used in the spirit production, the main source of income. Red fruits, with antioxidant potential, represent, also, a new market opportunity. The geographical isolation and extinction-recolonization dynamics are two factors causing strong genetic structure in metapopulations. We investigated how history, geography, and geoclimatic factors have affected population genetic structure, local adaptation, and, ultimately, its phylogeography. We examined patterns and levels of genetic diversity with nuclear microsatellites and cpDNA haplotypes in populations from across the species range. Under the project ARBUTUS (PTDC/AGR-FOR/3746/2012, Arbutus unedo plants and products quality improvement for the agro-forestry sector) 30 trees were selected, georeferenced, and leaves sampled, in 15 natural populations distributed throughout the country. With GIS tools, the stands were ecologically characterized, at a local scale, using lithology, topography, soil type, vegetation and wildfires records. This data was further used to distinguish Local Landscape Units (LLU) associated with each population. The populations were further clustered using large scale biogeographic and vegetation successions information and, this a priori hierarchy, together with the genetic structure information, was used to explain the species phytogeography. We aimed at finding the historical population demographic scenarios to explain the current patterns of genetic structure and diversity unfold for the species. The obtained information will be used in the species improvement, management and design of conservation programs.

Mediterranean forests are fragile ecosystems vulnerable to recent global warming and reduction of precipitation, and a long-term negative effect is expected on vegetation with increasing drought and in areas burnt by fires. We investigated the spatial distribution of genetic variation of Arbutus unedo in the western Iberia Peninsula, using plastid markers with conservation and provenance regions design purposes. This species is currently undergoing an intense domestication process in the region, and, like other species, is increasingly under the threat from climate change, habitat fragmentation and wildfires. We sampled 451 trees from 15 natural populations from different ecological conditions spanning the whole species' distribution range in the region. We applied Bayesian analysis and identified four clusters (north, centre, south, and a single-population cluster). Hierarchical AMOVA showed higher differentiation among clusters than among populations within clusters. The relatively low within-clusters differentiation can be explained by a common postglacial history of nearby populations. The genetic structure found, supported by the few available palaeobotanical records, cannot exclude the hypothesis of two independent A. unedo refugia in western Iberia Peninsula during the Last Glacial Maximum. Based on the results we recommend a conservation strategy by selecting populations for conservation based on their allelic richness and diversity and careful seed transfer consistent with current species' genetic structure.