A molecular and morphological investigation of the red seaweed genus Porphyra (Bangiales, Rhodophyta) in the northwest Atlantic.

摘要

To evaluate the possible occurrence of cryptic Porphyra taxa in the Northwest Atlantic, extensive field collections were made during winter and spring periods when relatively few previous collections had been made. Approximately 100 different sites extending from Chance Harbor, New Brunswick, Canada to Rye, New York, USA, were sampled during multiple years (2001-2005). Historical specimens from several herbaria (NHA, FH, BM, WTU, MICH, US) were also examined for possible cryptic taxa. A combination of morphological and molecular tools was used to screen both recent and historical collections.; Sequences from the plastid-encoded, ribulose-1, 5-bisphosphate carboxylase-oxygenase large subunit (rbcL) gene and rbcL- rbcS spacer, the nuclear ribosomal small subunit (SSU), and internal transcribed spacer 1 (ITS1) regions were compared with other Porphyra taxa sequences available on GenBank. Sequences from four taxa were found to match Pacific taxa, with three of these having not been previously reported for the Northwest Atlantic (i.e. P. rediviva Stiller & Waaland, P. yezoensis f. narawaensis Miura, P. katadae Miura). In addition, five previously undescribed taxa, with unique rbcL, SSU, and ITS1 sequences were discovered.; Porphyra rediviva, which was previously described from the Pacific, could not be morphologically or ecologically distinguished from P. purpurea (Roth) C. Agardh. Additionally, the rbcL and ITS1 sequences from the nomenclatural type specimens of both species were identical, providing compelling evidence for the synonymization of P. rediviva under the older named taxon, P. purpurea. As there was an equal amount of molecular variation within both the Atlantic and Pacific populations of P. purpurea, the designation of a parent population was unclear. With this synonym, the number of known monostromatic species occurring in the Northwest Atlantic having male/female gametangia on separate longitudinal "halves" of the blade includes P. purpurea, P. birdiae, and P. katadae. While molecular differences among these three species are distinct, morphological and ecological features are less clear. However, differences between these taxa are more apparent if combinations of both morphological and ecological characteristics are used. For example, by combining blade thickness and color, P. katadae can be delineated from both P. purpurea and P. birdiae , while a comparison of distributional patterns show a clear distinction between more northern P. birdiae and southern P. katadae.; Despite the recent report of Porphyra yezoensis f. yezoensis from a single site in New Hampshire, USA, molecular screenings of specimens from across the region provides strong evidence of a once continuous distribution from mid-Maine to western Long Island Sound. In addition to the populations of P. yezoensis f. yezoensis in New England, three populations of this taxon were found on the Gulf Coast of Texas, with one specimen dating back to the late 1960's. When comparisons of ITS1 sequences were made with Asian individuals, all New England specimens plus one Texas specimen had identical sequences to Japanese specimens, while the other two Texas populations showed a closer affinity to Chinese populations. Thus, the molecular evidence supports at least two introductions of P. yezoensis f. yezoensis to the Gulf Coast of Texas. The discovery of a second Asiatic cultivar, P. yezoensis f. narawaensis, in New England appears to be of more recent introduction than the established f. yezoensis as documented by its later development (1980's) and more circumscribed distribution that interrupts the continuous distribution of P. yezoensis f. yezoensis.; The ITS1 sequences of New England Porphyra yezoensis f. narawaensis populations show no variation and they are identical to as many as 16 commercial strains in Japan. Similarly, the distribution of another Asiatic species discovered in New England, P. katadae, is circumscribed, and it appears to be a recent i