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Genetic structure in Atlantic and Mediterranean populations of Octopus vulgaris.

Hermosilla C1,2, Rocha F1 & Quesada H2.

1Departamento de Ecología y Biología Animal, Universidad de Vigo.

2Departamento de Bioquímica, Genética e Inmunología, Universidad de Vigo.

We examined the geographic pattern of genetic variation in European populations of Octopus vulgaris sequencing a mitochondrial DNA fragments of 986 bp encompassing the ND1-ND6 genes (12 populations, n = 240), in an attempt to understand the roles of dispersal and vicariance in this species. Phylogenetic analysis revealed the existence of two divergent mitochondrial lineages, one lineage occurring mainly in Atlantic populations, and the second lineage occurring mainly in Mediterranean populations. The relative frequencies of haplotypes belonging to each lineage in the different populations show a steep West–East clinal distribution with maximal mixture of the two lineages in the Gibraltar strait. The populations fell into three geographic assemblages, which we designated as Atlantic, Western and Eastern Mediterranean. This phylogeographical pattern suggests allopatric differentiation of the two lineages in separate Atlantic and Mediterranean refugia, followed by range expansion leading to secondary contact and admixture between Atlantic and Mediterranean phylogroups. Linear regression of pairwise estimates of interpopulation differentiation (FST/[1-FST]) on interpopulation geographic distance revealed some evidence of isolation by distance within Atlantic and Mediterranean phylogroups but not between them, consistent with historical vicariance between but not within these regions. Our results argue for the management of the species as two separate stocks.

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