Mitogenomic sequences better resolve stock structure of southern Greater Caribbean green turtle rookeries

Abstract

Analyses of mitochondrial control region polymorphisms have supported the presence of several demographically independent green turtle (Chelonia mydas) rookeries in the Greater Caribbean region. However, extensive sharing of common haplotypes based on 490-bp control region sequences confounds assessment of the scale of natal homing and population structure among regional rookeries. We screened the majority of the mitochondrial genomes of 20 green turtles carrying the common haplotype CM-A5 and representing the rookeries of Buck Island, St. Croix, United States Virgin Islands (USVI); Aves Island, Venezuela; Galibi, Suriname; and Tortuguero, Costa Rica. Five single-nucleotide polymorphisms (SNPs) were identified that subdivided CM-A5 among regions. Mitogenomic pairwise φ(ST) values of eastern Caribbean rookery comparisons were markedly lower than the respective pairwise F(ST) values. This discrepancy results from the presence of haplotypes representing two divergent lineages in each rookery, highlighting the importance of choosing the appropriate test statistic for addressing the study question. Haplotype frequency differentiation supports demographic independence of Aves Island and Suriname, emphasizing the need to recognize the smaller Aves rookery as a distinct management unit. Aves Island and Buck Island rookeries shared mitogenomic haplotypes; however, frequency divergence suggests that the Buck Island rookery is sufficiently demographically isolated to warrant management unit status for the USVI rookeries. Given that haplotype sharing among rookeries is common in marine turtles with cosmopolitan distributions, mitogenomic sequencing may enhance inferences of population structure and phylogeography, as well as improve the resolution of mixed stock analyses aimed at estimating natal origins of foraging turtles.