Cuttlefish (Sepia officinalis L., 1758) populations along turkish coast lines of the Aegean and Mediterranean seas: Genetic structure and population dynamics

Along with the increase of world population, increasing food demand cause fishing pressure on marine resources and decline in fish stocks. To provide the food demand, commercial fishing sector is in search of alternative food sources. Cephalopod species which have a the potential of being the solution for the problem find the opportunity to increase their population sizes without the predatory pressure of fishes. To avoid the problems faced during the exploitation of fishes, it is also important to provide a sustainable fisheries management for cephalopod fisheries with a supportive knowledge on their biological features and the geographic limits. As a cephalopod species Sepia officinalis L. 1758 is distributed in our seas and has an important place in fisheries markets. Also this species is an ideal candidate for testing physical and evolutionary factors restricting gene flow in its distribution area. The aim of the thesis is to determine the genetic variation and population structuring of common cuttlefish around Turkish coasts of the Mediterranean and the Aegean Seas as a model species with molecular methods.mtCOI sub units of 225 individuals of S. officinalis from 22 sampling locations were analyzed to characterize the present and past population dynamics. Besides five polymorphic microsatellite loci of 341 individuals from five localities were analyzed to evaluate the genetic relationships between common cuttlefish populations.As a result of computer analyses of mtCOI gen region, four phylogroups two originated from the Aegean Sea and two originated from the Mediterranean Sea, were determined. Four semi conductive barrier regions, effecting gene flow through the sampling areas, had been determined from genetic differentiation between the sapling regions. First two of these barriers, originating from the sudden depth, were found to be located between Marmaris ? Finike sampling areas and caused separation of haplotype groups located in the Mediterranean and the Aegean Sea. This barrier region seemed to be formed by the suitability of Mersin Bay and Iskenderun Bay as a good living area for these organisims and the effect of sudden increase of depth towards the western part. Eastern part of this barrier region showed remarkably different genetic characteristics. The last barrier region was found to be located in İzmir Bay and seemed to separate this region from the rest of the sampling areas.Separation of the Aegean Sea and the Mediterranean Sea was also observed with the results of the analyses of species specific five polymorphic microsatellite regions. Besides three different common cuttlefish populations have been determined through the stud area. The first population was found to be located in Mersin Bay and Antalya Bay, the second population was located between Marmaris and Seferihisar sampling locations and the last population was located in Enez sampling location in northern part of the Aegean Sea.It is determined that on the contrary of previous studies, the structure of common cuttlefish populations formed under the effect of depth changes, not because of the genetic isolation by distance. Analyses of demographic history of four phylogroups revealed that these phylogroups expanded their sizes upon the reestablishment of the sustainable environmental conditions after the last glacial period.