Mitochondrial microsatellite sequences improve the resolution of genetic structure in western Greater Caribbean green turtle nesting populations

Understanding the spatial scale of population processes is critical for contextualizing monitoring and prioritizing conservation actions. Green turtle ( Chelonia mydas ) abundance in the Greater Caribbean (GC) region is rebounding from centuries of overexploitation, but recovery trajectories vary among nesting populations. Maternally inherited mitochondrial DNA control region (CR) markers can link juveniles to their source populations, providing spatial ecology context for interpreting differential population trends. However, CR haplotype CM-A3 is shared across all western GC sites, limiting resolution. In this study, 387 females from Tortuguero, Costa Rica, the largest nesting population in the western Atlantic, were reanalyzed through sequencing of an expanded (817-base pair) CR fragment and the mitochondrial short tandem repeat (mtSTR) array. Variation in mtSTR sequences yielded 12 Tortuguero CM-A3 haplotypes. No structure was detected in mtSTR haplotype frequencies spatially or temporally within the Tortuguero rookery. In GC regional comparisons, Tortuguero CM-A3 mtSTR haplotype frequencies were significantly different from those of published Cayman Islands and major Florida nesting populations. This improved resolution of genetic structure reinforces the inference of demographic discreteness of these nesting populations with respect to female natal homing. Furthermore, these refinements provide critical baseline data to reduce uncertainty in future mixed stock analyses. The mtSTR may prove useful in resolving stock structure and migratory connectivity in green turtles in other regions where common CR haplotypes are broadly distributed.