Different low-competition island habitats in Central Europe harbour similar levels of genetic diversity in relict populations of Galium pusillum agg. (Rubiaceae)
Abstract
Quaternary climatic oscillations are major determinants of biodiversity in Europe. Yet their consequences have rarely been assessed in species whose ranges were continuous in the cold spells but then became fragmented by expanding forest in the mid-Holocene into so-called interglacial refugia.
The Galium pusillum group (Rubiaceae), occupying various island-like habitats from the lowlands to the subalpine belt of Central Europe, is well suited for addressing the processes shaping genetic and cytological diversity of island populations and testing whether they leave distinct footprints in different habitat types. Using amplified fragment length polymorphism (AFLP) analysis and plastid sequences, we estimated the diversity and differentiation of 15 diploid and 44 tetraploid populations.
Although the frequency of ploidy levels differed between low-and high-elevation stands, genetic diversity was homogeneous across various habitat types and elevations. Overall, high diversity probably reflects long-term local persistence of the group that was followed by fragmentation into isolated but probably stable populations that do not show signs of diversity loss.
Moreover, hybridization pre-dating the contemporary fragmentation further increased overall diversity and was probably involved in the formation of a local subalpine endemic. In sum, our study shows that low-competition habitats of various substrates and elevations may play comparable roles in preserving distinct plant diversity.