POPULATION GENETIC-STRUCTURE AND GENE FLOW IN THE SEAGRASS POSIDONIA-OCEANICA ASSESSED USING MICROSATELLITE ANALYSIS

Microsatellite markers were utilized in a study on population genetic diversity of the endemic Mediterranean seagrass Posidonia oceanica (L. ) Delile. Five nuclear and one chloroplastic microsatellite markers de tected low levels of polymorphism in 6 populations sampled along the c oasts of Italy and Corsica (Western Mediterranean). The number of alle les per locus ranged from 1.5 to 2.0 and homozygosity was high within populations (f = 0.314). In the 120 individuals analyzed, only 32.5 % were distinct genotypes. Although gene flow seems to exist between geo graphically disjunct meadows (Nm = 1.55), private alleles were found i n some localities. In one population in particular (Lacco Ameno, Gulf of Naples), sampled at 2 different depths, a private allele was presen t only in the individuals of the shallow stand. Distance analysis iden tified genetic disjunction between the northern and the central-southe rn populations. This study indicates that (1) clonal growth is importa nt in the maintenance of P. oceanica populations, (2) limited inbreedi ng occurs in P. oceanica populations, which can be composed of clonal patches of different size, (3) gene flow exists, but genetic disjuncti on between populations can be influenced by local forces, and (4) micr osatellites are powerful markers in detecting genetic variability in c lonally reproducing species.