Amount and structure of intra- and interspecific genetic variation in the moss genus Polytrichum

Allozyme electrophoresis was used to determine amount and structure of genetic variation within and between five congeneric haploid moss species: Polytrichum formosum, P. commune, P. uliginosum, P. piliferum and P. juniperinum. For the different species, gene diversity within populations (H-S) ranged from very low (0.025) to moderate values (0.127), being, on average, lower than those observed for vascular plants and many other moss species. Polytrichum piliferum and P. juniperinum showed significantly higher levels of H-S than the other species examined, which possibly might be explained by sexual reproduction being more prevalent in these two species, that often live in more dynamic habitats, where turnover of individuals is more frequent. Genetic variability was observed to be structured in contrasting ways at different levels. At the intraspecific level genetic differentiation among populations of most Polytrichum species was low, F-ST less than or equal to 0.1, indicating a considerable degree of gene flow by wind-dispersed spores over substantial distances. At the interspecific level strong divergence, genetic identities being on average I=0.222, was observed between most species studied, despite low levels of divergence at the morphological level. These I-values are significantly lower than observed for congeneric vascular plant species and most congeneric bryophyte species. This suggests that the morphological conservatism is not due to lack of genetic variability and evolutionary potential.