PHYLOGEOGRAPHY AND POPULATION-STRUCTURE OF THE ATLANTIC AND MEDITERRANEAN GREEN TURTLE CHELONIA-MYDAS - A MITOCHONDRIAL-DNA CONTROL REGION SEQUENCE ASSESSMENT

Mitochondrial (mt) DNA sequences were analysed to resolve the phylogeo graphy and population genetic structure of Atlantic and Mediterranean populations of green turtles (Chelonia mydas). Analysis of sequence va riation over 487 base pairs of the control (D-loop) region identified 18 haplotypes among 147 individuals from nine nesting populations. Pai rwise comparisons of haplotype frequencies distinguished most nesting colonies, indicating significant genetic differentiation among rookeri es and a strong propensity for natal homing behaviour by nesting femal es. Comparison of control region sequence data to earlier restriction fragment length polymorphism (RFLP) data for the same individuals demo nstrates approximately a sixfold higher substitution rate in the 5' en d of the control region. The sequence data provide higher resolution b oth in terms of the number of mtDNA genotype variants and the phylogeo graphic relationships detected within the Atlantic region, and reveal a gene genealogy that distinguishes two groups of haplotypes correspon ding to (i) the western Caribbean and Mediterranean, and (ii) eastern Caribbean, South Atlantic and West Africa. The data suggest that phylo geographic patterns in the Atlantic Ocean may be interpreted in terms of female nest site fidelity and episodic dispersal events. The distri bution of mtDNA haplotypes within the region is thus explained by the geological and climatic alternations (glacial and interglacial) over t he last million years.