Population genetic structure and gene flow in the seagrass Posidonia oceanica assessed using microsatellite analysis

Abstract

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 detected low levels of polymorphism in 6 populations sampled along the coasts of Italy and Corsica (Western Mediterranean). The number of alleles per locus ranged from 1.5 to 2.0 and homozygosity was high within populations ((L)= 0.314). In the 120 individuals analyzed, only 32.5% were distinct genotypes. Although gene flow seems to exist between geographically disjunct meadows (Nm = 1.55), private alleles were found in some localities. In one population in particular (Lacco Ameno, Gulf of Naples), sampled at 2 different depths, a private allele was present only in the individuals of the shallow stand. Distance analysis identified genetic disjunction between the northern and the central-southern populations. This study indicates that (1) clonal growth is important in the maintenance of P. oceanica populations, (2) limited inbreeding occurs in P. oceanica populations, which can be composed of clonal patches of different size, (3) gene flow exists, but genetic disjunction between populations can be influenced by local forces, and (4) microsatellites are powerful markers in detecting genetic variability in clonally reproducing species.