Comparative Study of Seed Germination and Genetic Variation of Rare Endemic Rhinanthus osiliensis and Related Widespread Congener R. rumelicus (Orobanchaceae)

Abstract

Genetic diversity is affected by breeding systems, life history traits and the distribution of species. Generally, inbred species with restricted geographic distribution have lower genetic variation compared to common outbreeding plant species. Rhinanthus osiliensis is a narrow endemic growing in calcareous spring fens on the island Saaremaa, Estonia. Presumably the closest congener of R. osiliensis is R. rumelicus, which is widely distributed in Eastern and Central Europe and the Balkan Peninsula. Isozymes were used to describe the mating system, levels of genetic variation and differentiation between the populations of R. osiliensis and R. rumelicus. Genetic diversity was found to be higher in widespread R. rumelicus compared to the endemic R. osiliensis. A significantly higher inbreeding coefficient with a low germination rate indicated substantial autogamy in R. osiliensis, whereas R. rumelicus displayed a mixed mating mode with a moderate inbreeding coefficient and a high germination rate. The low genetic differentiation between R. osiliensis and R. rumelicus confirmed their close affinity and the short evolutionary period of both taxa after the postglacial colonization. Considering the restricted geographic range and inbreeding in populations of R. osiliensis, this species may face a loss of genetic variation in the future.