Phylogeography and genetic structure of the edible sea urchin Paracentrotus lividus (Echinodermata: Echinoidea) inferred from the mitochondrial cytochrome b gene FERRUCCIO MALTAGLIATI 1 *, GRAZIANO DI GIUSEPPE 2 , MICHELE BARBIERI 1 , ALBERTO CASTELLI 1 and FERNANDO DINI 2 1 Dipartimento di Biologia – Unità di Biologia Marina e Ecologia, Università di Pisa, Via Derna, 1, I-56126, Pisa, Italy 2 Dipartimento di Biologia – Unità di Protistologia-Zoologia, Università di Pisa, Via Volta, 4, I-56126, Pisa, Italy Received 4 February 2010; revised 17 March 2010; accepted for publication 17 March 2010 Phylogeographical analysis of Paracentrotus lividus was carried out by means of sequencing the mitochondrial cytochrome b gene (1143 bp) of 260 individuals collected at 22 Mediterranean and four Atlantic localities. Against a background of high haplotype diversity and shallow genetic structuring, we observed significant genetic divergence between the Adriatic Sea and the rest of the Mediterranean, as well as between the Mediterranean and the Atlantic sample groups. Furthermore, on the largest spatial scale, isolation by distance was detected. Three main haplogroups were identified by network and Bayesian assignment analyses. The relative proportions of haplogroups were different in the four regions considered, with the exception of Western and Eastern Mediterranean that showed a similar pattern. This result together with the outcome of Snn statistics, analysis of molecular variance and network analyses allowed to identify three weakly differentiated populations corresponding to the Atlantic, Western + Eastern Mediterranean, and Adriatic seas. Analyses of mismatch distribution and neutrality tests were consistent with the presence of genetic structuring and past demographic expansion(s). From a fisheries perspective, the results obtained in the present study are consistent with genetic sustainability of current exploitation; local depleted stocks are recurrently replenished by recruits that may have originated from nonharvested areas. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 910–923. ADDITIONAL KEYWORDS: assignment analysis – Atlantic – demographic history – dispersal – fisheries – gene flow – diversity – Mediterranean – sequencing. INTRODUCTION Most benthic marine invertebrates are characterized by sessile or sedentary adults and long-lived plank- tonic larval stages that may disperse over large dis- tances. Dispersal and gene flow generally act toward genetic homogenization of populations over broad geo- graphical distances (Scheltema, 1971); as a conse- quence, species with dispersive stages are expected to show abundant within-population and low between- population genetic variability. However, a bulk of literature has been produced on instances of lar- val retention and self-recruitment contributing to genetic structuring, even in marine species with free-swimming pelagic larvae (Edmands, Moberg & Burton, 1996; Becker et al., 2007). Furthermore, appropriate molecular markers may reveal footprints of past genetic structuring in apparently homoge- neous species as a reminder of historical events. The sea urchin Paracentrotus lividus (Lamarck, 1816) is an ecologically and economically important *Corresponding author. E-mail: fmaltagliati@biologia.unipi.it Biological Journal of the Linnean Society, 2010, 100, 910–923. With 5 figures © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 910–923 910