RELATIONSHIPS AMONG GEOGRAPHICALLY DISTANT POPULATIONS OF GRACILARIA-VERRUCOSA (GRACILARIALES, RHODOPHYTA) AND RELATED SPECIES

Organelle DNA from 11 populations of the marine red alga Gracilaria verrucosa (Hudson) Papenfuss or similar species, and one population of G. sordida W. Nelson as an outlier, was digested with five restriction endonucleases. Visual inspection, parsimonious tree construction and UPGMA cluster analyses of the resultant banding patterns revealed a G. verrucosa core group composed of strains form Wales, Norway, France, Argentina and Japan, with closely similar if not always identical profiles. A second well-defined group, containing two strains from England and a second one from France, was determined to belong to the related genus Gracilariopsis. Two populations, from Brazil and North Carolina, USA, consistently formed a third group in numerical analyses, but visual differences in their profiles and the UPGMA distances between them were sufficient to indicate that they represented different species. Finally, a population from British Columbia, Canada, confirmed a posteriori as being G. pacifica Abbott, provided yet another distinct restriction profile. Selected crossability tests revealed that strains with similar restriction profiles were interfertile, whereas those with dissimilar profiles were not. However, formation of functional cystocarps did not always lead to healthy, fecund tetrasporophytes, and this may reflect the minor differences observed in the restriction profiles of the parent strains.