Abstract
Restriction-site analyses of mitochondrial DNA (mtDNA) from the loggerhead sea turtle (Caretta caretta) reveal substantial phylogeographic structure among major nesting populations in the Atlantic, Indian, and Pacific oceans and the Mediterranean sea. Based on 176 samples from eight nesting populations, most breeding colonies were distinguished from other assayed nesting locations by diagnostic and often fixed restriction-site differences, indicating a strong propensity for natal homing by nesting females. Phylogenetic analyses revealed two distinctive matrilines in the loggerhead turtle that differ by a mean estimated sequence divergence p = 0.009, a value similar in magnitude to the deepest 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 Atlantic Ocean and the Mediterranean Sea from those in the Indian and Pacific oceans, genotypes representing the two primary loggerhead mtDNA lineages were observed in both Atlantic-Mediterranean and Indian-Pacific samples. We attribute this aspect of phylogeographic structure in Caretta caretta to recent interoceanic gene flow, probably mediated by the ability of this temperate-adapted species to utilize habitats around southern Africa. These results demonstrate how differences in the ecology and geographic ranges of marine turtle species can influence their comparative global population structures.
Highlights
Marine turtles of the family Cheloniidae encompass an ecological diversity that contrasts with their apparent morphological conservatism
To what extent might these and related ecological factors influence the phylogeography of marine turtle species? In the green turtle (Chelonia mydas), continental barriers have been of overriding importance in partitioning phylogenetic lineages (Bowen et al 1992)
Southern Africa may have been less formidable as a barrier to interoceanic gene flow in Caretta caretta than in the more tropical marine turtle species, a hypothesis that can be tested with molecular genetic data
Summary
In contrast to the green turtle, where a fundamental phylogenetic split distinguished turtles in the Atlantic Ocean and the Mediterranean Sea from those in the Indian and Pacificoceans, genotypes representing the two primary loggerheadmtDNA lineages wereobserved in both Atlantic-Mediterranean and Indian-Pacific samples We attribute this aspect of'phylogeographic structure in Caretta caretta to recent interoceanic gene flow, probably mediated by the ability of this temperate-adapted species to utilize habitats around southern Africa. The loggerhead has a more temperate distribution, including an Indian Ocean rookery (Natal, South Africa) within 1000 km of the South Atlantic Ocean (Hughes 1974a,b) Given this temperate habitat, southern Africa may have been less formidable as a barrier to interoceanic gene flow in Caretta caretta than in the more tropical marine turtle species, a hypothesis that can be tested with molecular genetic data. We assess mtDNA haplotype relationships among nesting colonies on a global scale to resolve recent evolutionary history and patterns of historical dispersal for this temperate marine reptile
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
