Molecular analysis reveals cryptic diversity and group I introns in Porphyra (Rhodophyta)

The red algal genus Porphyra is a prominent component of temperate marine floras worldwide and forms the basis of the multi-billion dollar nori seafood industry. As such it is among the most well studied of seaweeds with a long history of taxonomic scrutiny. Because of the large number of species, however, combined with its simple morphology and long evolutionary history, the systematics of Porphyra remains poorly understood. Little is known about intraspecific variability versus evolutionary convergence in traditional taxonomic characters making species identification difficult and rigorous phylogenetic analysis of the genus impossible. The purpose of the research described in this dissertation was to design an integrated research methodology, using molecular characters, to better define species limits and phylogenetic relationships in Porphyra. The small subunit rRNA (SSU rRNA) gene was amplified using the Polymerase Chain Reaction (PCR) and digested with restriction enzymes to produce species specific "riboprints". These riboprints were used to uncover hidden biodiversity and resulted in the description of a new species, P. rediviva (Stiller and Waaland submitted). Restriction sites were mapped on amplified SSU rDNA and used in phylogenetic analysis of selected Porphyra species. The results suggest that traditional systematic classification of Porphyra is artificial and that similar morphology can mask broad genetic divergence. During this research, group I introns were discovered in a geographic distribution and possible evolutionary history of these introns are discussed.