SINGLE-LOCUS MICROSATELLITES IN GRACILARIALES (RHODOPHYTA) - HIGH-LEVEL OF GENETIC-VARIABILITY WITHIN GRACILARIA-GRACILIS AND CONSERVATION IN RELATED SPECIES

Four single locus microsatellites identified in the red alga Gracilari a gracilis (Stackhouse) Steentoft, Irvine, et Farnham (Rhodophyta) wer e examined for allelic diversity at different spatial and taxonomic le vels. First, because simple morphological diagnostic characters are of ten missing within the Gracilariacae, we developed a simple and rapid method based on rDNA ITS size variation in order to verify the taxonom ic status of the samples used in this study. All European (including M editerranean samples), Argentinian, and Namibian samples used in our s tudy were confirmed to be a homogenous G. gracilis group. By contrast, our results on rDNA ITS sizes showed that Gracilaria from Japan, init ially identified as G. gracilis, was different from the rest of the G. gracilis group. Secondly, microsatellite polymorphism and conservatio n at the species level was tested on the worldwide collection of G. gr acilis and within a single population. The loci Gv1AAG and Gv1AAC show ed no allelic variation, whereas two others, Gv1CT and Gv2CT, were hig hly polymorphic. All microsatellite loci were conserved within G. Grac ilis, except in the sample from Japan. The taxonomic status of G. grac ilis from Japan is thus questionable. This study revealed a high level of within-population polymorphism (52 alleles for Gv1CT and 12 for Gv 2CT). Moreover; the combination of these two loci was shown to be very powerful for identifying individuals within a population, that is, 93 % of the individuals were characterized by a unique genotype. Finally, conservation of the four loci was tested in taxonomically related spe cies of Gracilaria (G. chilensis, G. pacifica, and G. tikvahiae) and t wo Gracilariopsis species (Gs. sp. and Gs. longissima). The results su ggest that the polymorphic locus Gv2CT may provide a valuable genetic marker within the different species of the Gracilariaceae.