The evolutionary history and global phylogeography of the green turtle ( Chelonia mydas )

Aim To examine the genetic structure and global phylogeography of the endangered green sea turtle, Chelonia mydas, in light of past climatic events and current conservation needs. Location Tropical and subtropical beaches around the world. Methods We analysed 386 base pairs of the mitochondrial (mt)DNA control region of 4,878 individual nesting green turtle samples from 127 rookeries globally. We used phylogeographic analysis to assess how demographic history, dispersal and barriers to gene flow have led to the current distribution of mtDNA lineages. Results We identified 11 divergent lineages that were tied to specific biogeographical regions. The phylogenetic analyses revealed an ancient origin for the species centred in the Indo-Pacific and more recent colonization of the Central/Eastern Pacific as well as the Atlantic Basin. Overall the phylogeographic structure was strong but with a clear pattern of regional connectivity among rookeries. A Large genetic separation was found where there were obvious barriers to dispersal such as between the Atlantic and Pacific oceans and across the Pacific Ocean, as well as less obvious barriers to dispersal. Admixture of mtDNA haplotype lineages was detected at latitudinal extremes across the Indian Ocean and western Pacific Ocean resulting in these areas being nucleotide diversity hotspots. The highest regional genetic diversity and high endemic richness was observed in the SW Pacific, NW Pacific, SW Indian and NW Indian oceans. Main conclusions Past climatic fluctuations greatly affected the distribution of genetic diversity in the highly migratory green turtle. Our data suggest that past climatic events influenced local populations in different ways and the species appears to have survived the last glaciations in multiple glacial refugia.