Allozyme genetic variability and gene flow in Octopus vulgaris (Cephalopoda, Octopodidae) from the Mediterranean Sea

Allozyme electrophoresis was used to investigate genetic variability at twenty putative enzyme-coding loci within and between eight samples of Octopus vulgaris and one of O. salutii collected in the Mediterranean. The mean number of alleles per locus, percentage of polymorphic loci, observed and expected heterozygosity (±SE) of O. vulgaris populations were A = 1.04 ± 0.05 to 1.16 ± 0.08, P₉₉ = 20 to 45%, H _o = 0.035 ± 0.022 to 0.114 ± 0.036, H _e = 0.043 ± 0.026 to 0.136 ± 0.041, respectively. Pairwise Nei's genetic distances detected in O. vulgaris were typical of conspecific populations (D = 0.001 ± 0.000 to 0.089 ± 0.014), whereas genetic distances between O. vulgaris and O. salutii samples were characteristic of congeneric species (D = 1.076 ± 0.072 to 1.152 ± 0.077). The coancestry coefficient revealed low genetic heterogeneity within western Mediterranean region, whereas strong substructuring was detected in both the total data set and in the two eastern populations. A Mantel test failed to reveal isolation-by-distance at both Mediterranean and regional scales. Our results suggest that O. vulgaris in the Mediterranean is structured according to the island model in a background of high gene flow, with a sharp discontinuity between the western and eastern basins, as revealed by cluster analysis and multidimensional scaling. The effectiveness of paralarval dispersal may account for the moderate genetic heterogeneity detected within the western Mediterranean.