Assessment of current genetic structure from local to geographic scales indicates brake down of historically extensive gene flow in the dry grassland species Scabiosa canescens Waldst. & Kit. (Dipsacaceae)

Aim: Species-rich dry grasslands have declined drastically in recent decades leading to spatial isolation of associated species. This can disrupt gene flow leading to genetic erosion, inbreeding and increased differentiation. Using Scabiosa canescens as a case for a threatened central European species confined to dry grasslands, we investigate the genetic consequences of spatial and functional isolation. In particular, inbreeding and loss of genetic diversity are expected to be more pronounced in populations at the northern margin of the sampling area due to more intense agriculture, less suitable habitat and potential post-glacial colonization from the south. Location: Germany. Methods: We genotyped 563 individuals at 10 microsatellite loci from 22 populations across the species' range in Germany. We analyse spatial genetic structure and patterns of isolation by distance (IBD) at multiple scales. Further, we identify latitudinal and altitudinal patterns of genetic diversity and inbreeding. Results: We found strong population differentiation but no IBD up to at least 200 km. Levels of inbreeding were positively correlated with latitude and tended to decline with altitude. An integration of altitude and latitude into temperature-corrected altitude (CA) was positively correlated with genetic diversity. Populations in the Upper Rhine Valley appear to have a distinct ancestry. Main conclusions: We interpret the strong population differentiation combined with no IBD up to at least 200 km as a sign for disrupted extensive gene flow. A trend for reduced genetic diversity towards the northern populations occurring at lower altitudes is probably driven by more intense land use but cannot be conclusively distinguished from other potential factors such as a more recent colonization history. Apart from the distinct Upper Rhine Valley populations, our findings suggest that assisted gene flow up to 100 km would mitigate genetic differentiation, inbreeding and loss of genetic diversity caused by disrupted long-distance dispersal.