Formerly common plant species are expected to be particularly susceptible to recent habitat fragmentation. We studied the population genetics of 19 recently fragmented Saxifraga granulata populations (max. distance 61 km) in Luxembourg and neighbouring Germany using RAPD markers and a common garden experiment. We assessed (1) the relationships between plant fitness, quantitative genetic variation, molecular genetic variation and population size, and (2) the relative importance of genetic drift and selection in shaping genetic variation. Molecular genetic diversity was high but did not correlate with population size, habitat conditions or with plant performance. Genetic differentiation was low (F_ST = 0.079 ± 0.135) and there was no isolation by distance. Longevity, clonality and the long-lived seed bank of S. granulata may have prevented strong genetic erosion and genetic differentiation among populations. However, genetic distinctness increased with decreasing genetic diversity indicating that random genetic drift occurred in the studied populations. Quantitative and molecular genetic variation were correlated and their differentiation (Q_ST vs. F_ST) among S. granulata populations was similar, suggesting that mainly random processes have shaped the quantitative genetic differentiation among populations. However, pairwise quantitative genetic distances increased with geographic and climatic distances, even when adjusted for molecular genetic distances, indicating diversifying selection. Our results indicate that long-lived clonal species may be buffered at least temporarily against the negative effects of fragmentation. The relationship between quantitative genetic and geographic distance may be a more sensitive indicator of selection than Q_ST - F_ST differences.

In 2003, we selected 15 plants along a 15 m transect in each of 19 populations in Luxembourg and in the neighbouring state of Rheinland-Pfalz in Germany for a study on the genetic structure of the populations. We counted the number of flowers in the field, took leaf samples for a RAPD molecular genetic analysis and collected seeds for the cultivation of plants in a common garden and the subsequent measurement of quantitative traits.

This dataset includes individual genotype data based on the presence or absence of reliable bands of RAPD amplification products at 52 polymorphic band positions for 247 Saxifraga granulata samples collected in 19 populations, the measurements of quantitative traits on F1 plants cultivated in a common garden from seeds collected in 19 populations, data on quantitative genetic, molecular genetic, geographic and climatic variables of the populations as well as the pairwise climatic, geographic, quantitative genetic and molecular genetic distances between the 19 populations. Data are stored in separate files which relate to each other via the key variable Popno (the number of a population).

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