POPULATION-STRUCTURE OF LOGGERHEAD TURTLE (CARETTA-CARETTA) NESTING COLONIES IN THE ATLANTIC AND MEDITERRANEAN AS INFERRED FROM MITOCHONDRIAL-DNA CONTROL REGION SEQUENCES

Mitochondrial (Int) DNA control region sequences were analyzed for 249 Atlantic and Mediterranean loggerhead turtles (Caretta caretta Linnae us, 1758) to elucidate nesting population structure and phylogeographi c patterns. Ten haplotypes were resolved among individuals sampled bet ween 1987 and 1993, from ten major loggerhead nesting areas in the reg ion. Two distinct phylogenetic lineages were distinguished, separated by an average of 5.1% sequence divergence. Haplotype frequency compari sons between pairs of populations showed significant differentiation b etween most regional nesting aggregates and revealed six demographical ly independent groups, corresponding to nesting beaches from: (1) Nort h Carolina: South Carolina, Georgia and northeast Florida, USA; (2) so uthern Florida, USA; (3) northwest Florida, USA; (4) Quintana Roo, Mex ico; (5) Bahia, Brazil; and (6) Peloponnesus Island, Greece. The distr ibution of mtDNA haplotypes is consistent with a natal homing scenario , in which nesting colonies separated by a few hundred kilometers repr esent isolated reproductive aggregates. However, a strong exception to this pattern was observed in the first group defined by mtDNA data (N orth Carolina to northeast Florida), which included samples from four nesting locations spread across thousands of kilometers of coastline. These locations were characterized by a single haplotype in 104 out of 105 samples, providing inadequate resolution of population divisions. In view of the subdivisions observed elsewhere, we attribute the lack of differentiation between North Carolina and northeast Florida to re cent colonization of these warm temperate coastlines (after the Wiscon sin glaciation) not to ongoing gene flow among spatially distinct nest ing locations. The relationships among observed haplotypes suggest a b iogeographic scenario defined by climate, natal homing, and rare dispe rsal events. The redefined relationships among nesting aggregations in the western Atlantic region (southeastern USA and adjacent Mexico) pr ompt a reconsideration of management strategies for nesting population s and corresponding habitats in this region.