Hawksbill sea turtle genetics: Determining genetic relationships among Caribbean hawksbill nesting populations and origin of juveniles sampled at Buck Island
Dates
Start Date
2014-10
End Date
2015-09
Summary
Hawksbill turtle populations have been severely depleted. We compared genetic diversity of females nesting at Buck Island Reef National Monument, St. Croix, US Virgin Islands with juveniles foraging in the region using standard control region sequences supplemented with nuclear microsatellite data. Four 760-base pair haplotypes were present among the expanded rookery samples: EiA01, EiA03, EiA11, and EiA20. In contrast, 61 foraging juveniles yielded 14 haplotypes, including three orphan haplotypes that have only been described from foraging aggregations and one novel haplotype. The haplotype frequencies for the foraging aggregation were distinct from those described from the Gulf of Mexico and Florida coast but not different from the [...]
Summary
Hawksbill turtle populations have been severely depleted. We compared genetic diversity of females nesting at Buck Island Reef National Monument, St. Croix, US Virgin Islands with juveniles foraging in the region using standard control region sequences supplemented with nuclear microsatellite data. Four 760-base pair haplotypes were present among the expanded rookery samples: EiA01, EiA03, EiA11, and EiA20. In contrast, 61 foraging juveniles yielded 14 haplotypes, including three orphan haplotypes that have only been described from foraging aggregations and one novel haplotype. The haplotype frequencies for the foraging aggregation were distinct from those described from the Gulf of Mexico and Florida coast but not different from the neighboring Mona Island, Puerto Rico aggregation. Rookery sources for the juvenile foraging aggregation were not clear. Mixed stock analyses suggested a large contribution from the Colombian coast, but the presence of orphan haplotypes and widespread sharing of EiA01 and EiA11 among several rookeries warrants caution in interpreting mixed stock analysis results. Microsatellite analyses in STRUCTURE treated all foraging individuals as belonging to a single genetic cluster. However, this apparent lack of structure should be interpreted with caution as the power to detect subtle structure in this study was likely limited by uneven rookery representation. The presence of a small number of individuals representing several different rookeries could dampen any signal of genetic structure. STRUCTURE analyses identified three genetic clusters among the Buck Island nesting females. Relatedness analysis in COLONY suggested that two of these clusters were each comprised of an inferred grandmother, her daughters, and granddaughters, with the third cluster representing all remaining individuals that did not belong to these two large maternal families. Further analyses in COLONY suggested that most EiA01 nesting females belonged to two maternal families and that the EiA20 females represented a single maternal family as well as two unrelated individuals. Overall, these data suggest that the majority of individual hawksbills nesting at Buck Island represent maternal families that have arisen from a small number of successful colonization events. This pattern could also reflect skew in reproductive fitness for a recovering population that has passed through a bottleneck. Apparently unrelated individuals may be the offspring of females with lower fitness, the descendants of more recent straying events, or may themselves be turtles that have strayed from other nesting populations. Relatedness analyses between Buck Island foragers and nesting females detected a single parentage match. Future work should address nuclear population structure through direct comparisons of rookery data sets to assess the signal strength of any structure and the possibility of assignment tests to overcome the haplotype sharing problem in mixed stock analysis of Caribbean hawksbills.
