Genetic population structure of the common sole, Solea solea Linnaeus, 1758 (Pisces, Pleuronectiformes) along the southern shores of the Mediterranean Sea (Tunisian coasts)

We studied the genetic differentiation among Solea solea populations, collected from both sides of the Siculo-Tunisian Strait (northeast and southeast Tunisian coasts), which is considered to be a boundary area between the eastern and western Mediterranean basins. Seven polymorphic enzyme loci (MDH-2*, MDH-3*, PGM*, PGI-1*, PGI-2*, GOT-2* and SOD*) were used in this study. Significant departure from the Hardy-Weinberg equilibrium, especially along the southeast Tunisian coast, was observed. Null alleles and inbreeding in populations subjected to overexploitation pressure can explain this result. No heterogeneity was detected between localities of both sides of the Siculo-Tunisian Strait, which reflects a continuous gene flow between northeast and southeast Tunisian coast populations. This result agrees with the biological characteristics of the species that favour the gene flow. In order to position Tunisian populations in the Mediterranean context, published data from eastern and western basins were integrated. Homogeneity was detected in the western Mediterranean basin and a high level of east-west differentiation was detected only with the extreme east Mediterranean populations (Aegean Sea and Egypt).