Evolutionary Processes and Hybridization within the Peat Mosses, Sphagnum

Sammanfattning: The aim of this thesis was to reveal details of the interspecific hybridization among bryophytes as exemplified by Sphagnum capillifolium and S. quinquefarium. I used a combination of morphometric and molecular methods, and cultivation experiments to (1) identify hybrid gametophytes, (2) reveal the contribution of each of the parents to the genomes of hybrids, (3) study the fertility of primary hybrid sporophytes, (4) explore the fitness of hybrids as compared to their parents. The results showed that S. capillifolium and S. quinquefarium are morphologically and genetically well differentiated. Hybrid sporophytes had low fertility. However, when the two species grow sympatrically, hybrid individuals are often present. They are morphologically and genetically more similar to S. capillifolium but possess a restricted number of traits and molecular markers of S. quinquefarium. A comparison with the genetic composition of hybrid gametophytes raised from primary hybrid sporophytes indicated that the natural hybrid gametophytes may be first generation recombinants. The inheritance of chloroplasts was found to be uniparental from the maternal plant. The growth experiment showed that Sphagnum hybrids are likely to survive in habitats with high and constant humidity, similar to the typical environment of S. quinquefarium. In such habitats they would be good competitors due to relatively high growth rate and high regeneration ability, enabling them to expand clonally and persist for long periods. The conclusion is, that interspecific gene flow in bryophytes, as exemplified by S. capillifolium and S. quinquefarium, may be more frequent and with farther reaching consequences then previously anticipated.