Philopatry of male marine turtles inferred from mitochondrial DNA markers

Abstract

Recent studies of mitochondrial DNA (mtDNA) variation among marine turtle populations are consistent with the hypothesis that females return to beaches in their natal region to nest as adults. In contrast, less is known about breeding migrations of male marine turtles and whether they too are philopatric to natal regions. Studies of geographic structuring of restriction fragment and microsatellite polymorphisms at anonymous nuclear loci in green turtle (Chelonia mydas) populations indicate that nuclear gene flow is higher than estimates from mtDNA analyses. Regional populations from the northern and southern Great Barrier Reef were distinct for mtDNA but indistinguishable at nuclear loci, whereas the Gulf of Carpentaria (northern Australia) population was distinct for both types of marker. To assess whether this result was due to reduced philopatry of males across the Great Barrier Reef, we determined the mtDNA haplotypes of breeding males at courtship areas for comparison with breeding females from the same three locations. We used a PCR-restriction fragment length polymorphism approach to determine control region haplotypes and designed mismatch primers for the identification of specific haplotypes. The mtDNA haplotype frequencies were not significantly different between males and females at any of the three areas and estimates of Fst among the regions were similar for males and females (Fst = 0.78 and 0.73, respectively). We conclude that breeding males, like females, are philopatric to courtship areas within their natal region. Nuclear gene flow between populations is most likely occurring through matings during migrations of both males and females through nonnatal courtship areas.

Figure 1

Sample locations of C. mydas populations in Australian waters. GoC, Bountiful Island, Gulf of Carpentaria; nGBR, Raine Island, northern Great Barrier Reef; sGBR, Heron Island, southern Great Barrier Reef. The feeding ground distributions of the nGBR and sGBR populations are depicted. The extent of feeding ground locations for the GoC is unknown.

Figure 2

Location and design of mismatch primers to generate diagnostic restriction sites in the mtDNA control region of C. mydas mtDNA. The TCR-5 or TCR-6 primers (26) were typically paired with the appropriate mismatch primer, though TCR-Ase and TCR-Hph were also used together. Shown are the template DNA sequence, the portion of the primer sequence containing the mismatch primer, and the sequences generated through PCR amplifications that indicate the presence (or absence) of the new restriction site.