Abstract
Previous genetic studies have demonstrated that natal homing shapes the stock structure of marine turtle nesting populations. However, widespread sharing of common haplotypes based on short segments of the mitochondrial control region often limits resolution of the demographic connectivity of populations. Recent studies employing longer control region sequences to resolve haplotype sharing have focused on regional assessments of genetic structure and phylogeography. Here we synthesize available control region sequences for loggerhead turtles from the Mediterranean Sea, Atlantic, and western Indian Ocean basins. These data represent six of the nine globally significant regional management units (RMUs) for the species and include novel sequence data from Brazil, Cape Verde, South Africa and Oman. Genetic tests of differentiation among 42 rookeries represented by short sequences (380 bp haplotypes from 3,486 samples) and 40 rookeries represented by long sequences (∼800 bp haplotypes from 3,434 samples) supported the distinction of the six RMUs analyzed as well as recognition of at least 18 demographically independent management units (MUs) with respect to female natal homing. A total of 59 haplotypes were resolved. These haplotypes belonged to two highly divergent global lineages, with haplogroup I represented primarily by CC-A1, CC-A4, and CC-A11 variants and haplogroup II represented by CC-A2 and derived variants. Geographic distribution patterns of haplogroup II haplotypes and the nested position of CC-A11.6 from Oman among the Atlantic haplotypes invoke recent colonization of the Indian Ocean from the Atlantic for both global lineages. The haplotypes we confirmed for western Indian Ocean RMUs allow reinterpretation of previous mixed stock analysis and further suggest that contemporary migratory connectivity between the Indian and Atlantic Oceans occurs on a broader scale than previously hypothesized. This study represents a valuable model for conducting comprehensive international cooperative data management and research in marine ecology.
Highlights
Marine vertebrates with cosmopolitan distributions often exhibit high dispersal and weak population structure across large spatial scales
One major haplogroup was represented by restriction fragment length polymorphism (RFLP) haplotype B from the southeastern USA, RFLP C from Brazil, and RFLP F from Oman
The second major haplogroup was represented by RFLP haplotype D from the southeastern USA, South Africa, and Greece; RFLP G from Japan, and RFLP H from Australia [13]
Summary
Marine vertebrates with cosmopolitan distributions often exhibit high dispersal and weak population structure across large spatial scales. Management Units (MUs) in this context are defined as rookeries with significant differences in mtDNA haplotype frequencies [14], and these populations are considered to be demographically isolated with respect to female natal recruitment. Nuclear gene flow can occur among distinct nesting populations as defined by mtDNA when turtles are admixed on foraging grounds or along migration corridors [15] This migration-mediated gene flow should not detract from classification of rookeries as independent nesting populations because female recruitment is what sustains rookeries demographically, irrespective of the level of migrationmediated gene flow [15]. Despite potential resolution issues with the use of mtDNA to infer demographic isolation of nesting populations [16,17], significant differences in mtDNA haplotype frequencies provide a reasonable first approximation for defining MUs until more direct demographic measures become available. Robust genetic data from natal rookeries are critical for assessing connectivity throughout the complex life cycle of this species
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