Allozyme differentiation in the cuttlefish Sepia officinalis (Mollusca : Cephalopoda) from the NE Atlantic and Mediterranean

The Atlantic-Mediterranean area has recently been proposed as a new phyloge ographical area on the basis of concordance of genetic differentiation patt erns observed in several marine species. However, additional taxa need to b e studied to establish the phylogeographical relationship between the Atlan tic and Mediterranean. Eleven samples of the cuttlefish Sepia officinalis a round the Iberian peninsula, one from the Canary Islands, and another from Fiumicino (Italy) were screened for 33 allozyme loci. Genetic variability w as low in all samples (H-e between 0.022 and 0.076). Intersample genetic di fferentiation was high (F-ST = 0.220), mainly because of genetic variation in the non-Iberian samples. One locus (PEPD*), diagnostic between the Itali an sample and ail others, suggests the possible existence of hitherto unrec ognized species or subspecies of Sepia in the Mediterranean Sea. The 11 Ibe rian samples exhibited moderate genetic differentiation (F-ST=0.100), which could be explained on the basis of genetic differentiation between Atlanti c and Mediterranean samples. Significant clines in allele frequencies were observed for five out of six polymorphic loci. These results support a mode l of secondary intergradation (i.e. secondary contact of populations that w ere previously differentiated in isolation) similar to that previously prop osed for other marine species from the Atlantic-Mediterranean area.