Genetic consequences of landscape change for rare endemic plants – A case study of Rhinanthus osiliensis

During the last hundred years European landscapes have experienced an extensive change in structure including a substantial loss of wetland habitats. In the current study we examined the influence of landscape change and current landscape composition on the genetic diversity of Rhinanthus osiliensis, a very rare endemic plant with narrow distribution range restricted to calcareous spring and species-rich fens in western part of the island of Saaremaa, Estonia. We observed very high inbreeding in some study populations of R. osiliensis. Furthermore, bottleneck analysis revealed that in fact all examined populations had experienced a severe decline in population size in the recent past. This result indicates that the high levels of inbreeding in R. osiliensis are not only the consequence of the mixed mating system common in this species, but may at least partly be attributed to habitat loss. Indeed, the analysis of landscape change revealed a substantial decrease in the area of mires during the last century in all study landscapes. Unexpectedly, current habitat availability did not influence the measures of genetic diversity. Nevertheless, the allelic richness of R. osiliensis was negatively affected by the amount of forests, which may have acted as a barrier for pollen flow in this insect-pollinated plant. We conclude that the populations of habitat-specialist rare plants such as R. osiliensis are endangered not only by the loss of habitats but also by other changes in landscape composition, e.g. afforestation, leading to strong declines in population size accompanied by genetic bottlenecks, decreased genetic diversity and high inbreeding.