Abstract
Understanding the connectivity among populations is a key research priority for species of conservation concern. Genetic tools are widely used for this purpose, but the results can be limited by the resolution of the genetic markers in relation to the species and geographic scale. Here, we investigated natal philopatry in green turtles (Chelonia mydas) from four rookeries within close geographic proximity (~200 km) on the Mediterranean island of Cyprus. We genotyped hypervariable mtSTRs, a mtDNA control region sequence (CR) and 13 microsatellite loci to genetically characterise 479 green turtles using markers with different modes of inheritance. We demonstrated matrilineal stock structure for the first time among Mediterranean green turtle rookeries. This result contradicts previous regional assessments and supports a growing body of evidence that green turtles exhibit a more precise level of natal site fidelity than has commonly been recognised. The microsatellites detected weak male philopatry with significant stock structure among three of the six pairwise comparisons. The absence of Atlantic CR haplotypes and mtSTRs amongst these robust sample sizes reaffirms the reproductive isolation of Mediterranean green turtles and supports their status as a subpopulation. A power analysis effectively demonstrated that the mtDNA genetic markers previously employed to evaluate regional stock identity were confounded by an insufficient resolution considering the recent colonisation of this region. These findings improve the regional understanding of stock connectivity and illustrate the importance of using suitable genetic markers to define appropriate units for management and conservation.
Highlights
Identifying demographically independent populations is central to the management and conservation of natural populations and a key research priority for species of conservation concern (Frankham, 2010; Rees et al, 2016; Wallace et al, 2011)
A ~800 bp fragment of the mitochondrial DNA control region was amplified by polymerase chain reaction (PCR) using the primer pair LCM15382 (5′-GCTTAACCCTAAAGCATTGG-3′) and H950 ( 5′-GTCTCGGATTTAGGGGTTT-3′) (Abreu-Grobois et al, 2006) in a 10 μl reaction consisting of 4 μl QIAGEN Multiplex PCR Master Mix (Qiagen®; including HotStar DNA Taq polymerase), 3 μl ddH2O, 1 μl of forward and reverse primers (5uM) and 1 μl of ~10 ng template DNA
Through the use of higher resolution mitochondrial DNA (mtDNA) markers, we reveal matrilineal stock structure amongst Mediterranean green turtle rookeries
Summary
Identifying demographically independent populations is central to the management and conservation of natural populations and a key research priority for species of conservation concern (Frankham, 2010; Rees et al, 2016; Wallace et al, 2011). Trying to define discrete management units based on the exact geographical specificity of natal homing in marine turtles has led to mixed conclusions dependent on the type and resolution of genetic markers (reviewed in Jensen et al, 2013; Komoroske et al, 2017) An example of this unclear resolution was raised when evaluating the fine scale regional genetic connectivity among populations of green turtles (Chelonia mydas) within the Mediterranean. This region has shown an unusual pattern, as a greater genetic structure has been detected with nuclear rather than mitochondrial DNA markers, and the largest regional rookeries situated in Turkey and Cyprus (Stokes et al, 2015) are suggested to be a single management unit (Bagda et al, 2012; Kaska, 2000). We provide more accurate data that can be applied within mixed stock analyses of foraging areas (Bolker et al, 2007) and fisheries bycatch data (Laurent et al, 1998)
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