Salvia officinalis survived in situ Pleistocene glaciation in 'refugia within refugia' as inferred from AFLP markers

Salvia officinalis is a perennial species, native and endemic to the Western Balkans and the Apennine Peninsula. Due to its medicinal and aromatic properties, it is used in pharmaceutical, cosmetic, and food industries. The main objectives of the study were to infer the genetic structure of S. officinalis populations in the northern and central parts of the eastern Adriatic coast, to detect the phylogeographical barriers among the putative microrefugia and to assess the genetic diversity among the resulting ancestral clusters. Twenty-five populations were assessed using amplified fragment length polymorphism markers. High polymorphism and high diversity within populations were typical for this outcrossing long-lived species. The Fitch-Margoliash tree based on Nei's genetic distance matrix showed that most of the populations tended to group in accordance with the geographical position of their collecting sites. Spatial analysis of the genetic diversity revealed a typical pattern of isolation by distance. Very low overall among-population differentiation and detection of only three private alleles indicate that there has been high gene flow among populations. By using Bayesian Analysis of Population Structure on population level, two distinct ancestral clusters were obtained. It is likely that these two ancestral clusters were separated for a longer period by Pleistocene glaciation, although the subsequent fast recolonization resulted in diminished genetic differences. High rarity of northern and southern populations of the investigated area indicates that S. officinalis presumably survived in both northern and southern microrefugia and expanded from there resulting in secondary contact zones, characterized by lower rarity and equal genetic diversity.