GLOBAL PHYLOGEOGRAPHY OF THE LOGGERHEAD TURTLE (CARETTA-CARETTA) AS INDICATED BY MITOCHONDRIAL-DNA HAPLOTYPES

Restriction-site analyses of mitochondrial DNA (mtDNA) from the logger head sea turtle (Caretta caretta) reveal substantial phylogeographic s tructure among major nesting populations in the Atlantic, Indian, and Pacific oceans and the Mediterranean sea. Based on 176 samples from ei ght nesting populations, most breeding colonies were distinguished fro m other assayed nesting locations by diagnostic and often fixed restri ction-site differences, indicating a strong propensity for natal homin g by nesting females. Phylogenetic analyses revealed two distinctive m atrilines in the loggerhead turtle that differ by a mean estimated seq uence divergence p = 0.009, a value similar in magnitude to the deepes t intraspecific mtDNA node (p = 0.007) reported in a global survey of the green sea turtle Chelonia mydas. In contrast to the green turtle, where a fundamental phylogenetic split distinguished turtles in the At lantic Ocean and the Mediterranean Sea from those in the Indian and Pa cific oceans, genotypes representing the two primary loggerhead mtDNA lineages were observed in both Atlantic-Mediterranean and Indian-Pacif ic samples. We attribute this aspect of phylogeographic structure in C aretta caretta to recent interoceanic gene flow, probably mediated by the ability of this temperate-adapted species to utilize habitats arou nd southern Africa. These results demonstrate how differences in the e cology and geographic ranges of marine turtle species can influence th eir comparative global population structures.