Phylogeography and population structure of the Atlantic and Mediterranean green turtleChelonia mydas: a mitochondrial DNA control region sequence assessment

Abstract

Mitochondrial (mt) DNA sequences were analysed to resolve the phylogeography and population genetic structure of Atlantic and Mediterranean populations of green turtles (Chelonia mydas). Analysis of sequence variation over 487 base pairs of the control (D-loop) region identified 18 haplotypes among 147 individuals from nine nesting populations. Pairwise comparisons of haplotype frequencies distinguished most nesting colonies, indicating significant genetic differentiation among rookeries and a strong propensity for natal homing behaviour by nesting females. Comparison of control region sequence data to earlier restriction fragment length polymorphism (RFLP) data for the same individuals demonstrates approximately a sixfold higher substitution rate in the 5' end of the control region. The sequence data provide higher resolution both in terms of the number of mtDNA genotype variants and the phylogeographic relationships detected within the Atlantic region, and reveal a gene genealogy that distinguishes two groups of haplotypes corresponding to (i) the western Caribbean and Mediterranean, and (ii) eastern Caribbean, South Atlantic and West Africa. The data suggest that phylogeographic patterns in the Atlantic Ocean may be interpreted in terms of female nest site fidelity and episodic dispersal events. The distribution of mtDNA haplotypes within the region is thus explained by the geological and climatic alternations (glacial and interglacial) over the last million years.

Movement patterns of marine turtles in the Mediterranean Sea: a review

“…A limited number of individuals disperse as far as the Ionian, Adriatic and Tyrrhenian Seas (Lazar et al 2004;Bentivegna et al 2011). The Mediterranean green turtle population shows a genetic divergence from the Atlantic populations (Encalada et al 1996), indicating a degree of isolation, and is affected by strong anthropogenic pressures primarily represented by incidental catches in fishery activities (Casale 2011). Like loggerheads, green turtles feed upon pelagic prey in the first period of their life but then shift to a herbivorous diet, feeding upon benthic seagrasses and algae (Bjorndal 1997).…”

Advances in the Application of Genetics in Marine Turtle Biology and Conservation

“…In particular, within the eastern Caribbean, the large rookeries of Suriname and Aves Island are nearly fixed for haplotype Frontiers in Marine Science | www.frontiersin.orgCM-A5 (Encalada et al, 1996), which is also detected at low frequency in the Tortuguero, Costa Rica rookery (Bjorndal et al, 2005). These patterns made it unclear if there is mixing among females nesting at these rookeries, or if there is population structure undetected by this particular marker.…”

“…Since that time, considerable progress has been made in refining the global population structure for this species through improved sampling efforts and development of genetic tools with increased power to detect population structure (Figure 1, Box 1). First, sequencing of the mtDNA control region (490 bp) from nine Atlantic and Mediterranean rookeries detected 6-fold greater genetic diversity compared to previous RFLP data (Encalada et al, 1996), significantly improving stock structure resolution and identifying at least six management units (MUs; see Box 2 for additional discussion of conservation units). Further progress was then made by increasing sampling sizes and coverage in the Florida nesting aggregation, clearly demonstrating that Florida is genetically distinct from the Quintana Roo, Mexico rookery and identifying at least two MUs within Florida, separated by the St. Lucie Inlet (Shamblin et al, 2015a).…”

“…Using data on mtDNA control region haplotypes, no population differentiation was detected between several green turtle rookery pairs despite being separated by several hundred kilometers. Examples included Aves Island and Suriname in the Northwest Atlantic (Encalada et al, 1996), the Brazilian archipelago rookeries of Fernando de Noronha and Atol das Rocas (Bjorndal et al, 2006), and the individual rookeries comprising the central and eastern Pacific stocks discussed above. Such observations provoke the important question: Is this apparent lack of population structure between rookeries within a region due to recent shared common ancestry, ongoing gene flow via female exchange across rookeries, or due to lack of resolution in the genetic markers employed?…”

“…Analysis of the mtSTR for CM-A13 turtles nesting and foraging in Florida yielded a shared repeat haplotype that was not among the 33 described thus far from the Mediterranean (Tikochinski et al, 2012), revealing that the foraging turtles most likely originated locally within the Greater Caribbean region (Shamblin et al, 2015b). In a second example, in the northern Greater Caribbean region, CM-A1 and CM-A3 are the dominant haplotypes shared among the rookeries of Quintana Roo, Mexico; Guanahacabibes Peninsula, Cuba; and Florida rookeries (Encalada et al, 1996;Ruiz-Urquiola et al, 2010;Shamblin et al, 2015a). An MSA of juvenile green turtles in Texas foraging grounds suggested a large Florida rookery contribution based on the presence of these haplotypes at high frequencies (Anderson et al, 2013).…”