Abstract
Sorbus domestica (Rosaceae) is one of the rarest deciduous tree species in Europe and is characterized by a scattered distribution. To date, no large-scale geographic studies on population genetics have been carried out. Therefore, the aims of this study were to infer levels of molecular diversity across the major part of the European distribution of S. domestica and to determine its population differentiation and structure. In addition, spatial genetic structure was examined together with the patterns of historic and recent gene flow between two adjacent populations. Leaf or cambium samples were collected from 17 populations covering major parts of the European native range from north-west France to south-east Bulgaria. Seven nuclear microsatellites and one chloroplast minisatellite were examined and analysed using a variety of methods. Allelic richness was unexpectedly high for both markers within populations (mean per locus: 3·868 for nSSR and 1·647 for chloroplast minisatellite). Moreover, there was no evidence of inbreeding (mean Fis = -0·047). The Italian Peninsula was characterized as a geographic region with comparatively high genetic diversity for both genomes. Overall population differentiation was moderate (FST = 0·138) and it was clear that populations formed three groups in Europe, namely France, Mediterranean/Balkan and Austria. Historic gene flow between two local Austrian populations was high and asymmetric, while recent gene flow seemed to be disrupted. It is concluded that molecular mechanisms such as self-incompatibility and high gene flow distances are responsible for the observed level of allelic richness as well as for population differentiation. However, human influence could have contributed to the present genetic pattern, especially in the Mediterranean region. Comparison of historic and recent gene flow may mirror the progress of habitat fragmentation in eastern Austria.
Highlights
The true service tree (Sorbus domestica), a light-demanding, insect-pollinated, rosaceous species, is distributed in the Mediterranean as well as in parts of France, Switzerland, Germany and Austria (Kutzelnigg, 1995), and has a very scarce occurrence in the British Isles
It is concluded that molecular mechanisms such as self-incompatibility and high gene flow distances are responsible for the observed level of allelic richness as well as for population differentiation
Comparison of historic and recent gene flow may mirror the progress of habitat fragmentation in eastern Austria
Summary
The true service tree (Sorbus domestica), a light-demanding, insect-pollinated, rosaceous species, is distributed in the Mediterranean as well as in parts of France, Switzerland, Germany and Austria (Kutzelnigg, 1995), and has a very scarce occurrence in the British Isles. Habitat fragmentation decreases the number of species (Mac Arthur and Wilson, 1967) and erodes genetic variation within and among populations due to increasing genetic drift, elevated inbreeding and reduced gene flow, and eventually increases the probability of local extinction of sub-populations (Young et al, 1996) This has been recently confirmed in Fagus sylvatica (Jump and Penuelas, 2006). From an evolutionary point of view, it can be assumed that this tree species is well adapted to a patchy habitat structure and that these patches are part of a metapopulation dynamic (Rotach, 2003) These dynamics are characterized through their demographic and genetic stochasticity where the degree of fragmentation and the size of ther remaining populations play a key role for the risk of local extinction (Hanski, 1998). Spatial genetic structure was examined together with the patterns of historic and recent gene flow between two adjacent populations
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