Global phylogeography of the leatherback turtle (Dermochelys coriacea)

Analyses of mitochondrial (mt) DNA control region sequences from 175 leathe rback turtles Dermochelys coriacea from 10 nesting colonies revealed shallo w phylogenetic structuring of maternal lineages on a global scale. Eleven h aplotypes were observed, and mean estimated sequence divergence, p = 0.0058 1, is much lower than the deepest nodes reported in global mtDNA surveys of the green turtle Chelonia mydas, loggerhead Caretta caretta, and ridley tu rtles Lepidochelys spp. The leatherback turtle is the product of an evoluti onary trajectory originating at least 100 million years ago, yet the intras pecific phylogeny recorded in mitochondrial lineages may trace back less th an 900000 years. The gene genealogy and global distribution of mtDNA haplot ypes indicate that leatherbacks may have radiated from a narrow refugium, p ossibly in the Indian-Pacific during the early Pleistocene glaciation. Anal ysis of haplotype frequencies revealed that nesting populations are strongl y subdivided globally (F-ST = 0.415), and within ocean basins (F-ST = 0.203 -0.253), despite the leatherback's highly migratory nature. Within the Atla ntic significant differences in haplotype frequency distributions and Nm Va lues <2 are observed in pairwise comparisons between St. Croix (U.S. Virgin Islands) and mainland Caribbean populations, and between Trinidad and the same mainland populations. These findings provisionally support the natal h oming hypothesis for leatherback turtles, although several proximal nesting populations were indistinguishable, suggesting recent colonization or less precise natal homing behaviour than documented for other marine turtle spe cies. The evidence of natal homing, manifested on ecological time scales, m ay be erased in some populations by rapid rookery turnover resulting from c limatic fluctuation and the ephemeral nature of nesting habitat on a geolog ical time scale. The evolutionary effective population size (N-e) is estima ted from mtDNA data to be between 45 000 and 60 000, a value that exceeds c urrent global census estimates of 26 000 to 43 000 adult females.