Genetic variation in two cryptic species of the rare fen moss Hamatocaulis vernicosus in the Czech Republic

Patterns in the genetic variation of two cryptic species (termed also clades) of the rare moss Hamatocaulis vernicosus in the Czech Republic were studied using two sets of polymorphic microsatellite loci, developed for each cryptic species separately with respect to cross-amplification failure. Reproductive isolation of the morphologically indistinguishable and commonly co-occurring species was confirmed not only by the absence of cross-compatibility in all but five of the used primers, but also by the obvious absence of gene flow at localities where both cryptic species co-occurred. The genetic diversity expressed in terms of the number of genotypes and Shannon diversity index was higher in clade 1 (southern cryptic species), which is more common in the region, than in clade 2 (northern cryptic species). Both cryptic species also differed in structure of their genetic diversity. While in clade 2, 84% of the variability was among populations, the level of inter-population variability was only 51% in clade 1. The high genetic isolation of populations indicates the detrimental effect habitat fragmentation has had on central European fens. The level of sexual reproduction at most localities was low, especially in the larger clones of clade 2. The effect of genetic pauperization seems to be counteracted by somatic mutations, which were recorded at several localities.