Biology Faculty Articles

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Frontiers in Marine Science


island populations, connectivity, coastal sharks, shark reef marine reserve, population genomics, dispersal barriers





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The bull shark (Carcharhinus leucas) is a large, mobile, circumglobally distributed high trophic level predator that inhabits a variety of remote islands and continental coastal habitats, including freshwater environments. Here, we hypothesize that the barriers to dispersal created by large oceanic expanses and deep-water trenches result in a heterogeneous distribution of the neutral genetic diversity between island bull shark populations compared to populations sampled in continental locations connected through continuous coastlines of continental shelves. We analyzed 1,494 high-quality neutral single nucleotide polymorphism (SNP) markers in 215 individual bull sharks from widespread locations across the Indian and Pacific Oceans (South Africa, Indonesia, Western Australia, Papua New Guinea, eastern Australia, New Caledonia, and Fiji). Genomic analyses revealed partitioning between remote insular and continental populations, with the Fiji population being genetically different from all other locations sampled (FST = 0.034–0.044, P < 0.001), and New Caledonia showing marginal isolation (FST = 0.016–0.024, P < 0.001; albeit based on a small sample size) from most sampled sites. Discriminant analysis of principal components (DAPC) identified samples from Fiji as a distinct cluster with all other sites clustering together. Genetic structure analyses (Admixture, fastStructure and AssignPOP) further supported the genetic isolation of bull sharks from Fiji, with the analyses in agreement. The observed differentiation in bull sharks from Fiji makes this site of special interest, as it indicates a lack of migration through dispersal across deep-water trenches and large ocean expanses.


The project was supported by the Ausbildungs-Stiftung fuer den Kanton Schwyz und die Bezirke See und Gaster (Kanton St. Gallen, Switzerland), the Shark Foundation Switzerland and Pacific Scholarship for Excellence in Research & Innovation of the University of the South Pacific. Grant SRT/F1006-R1001-71502-663 was given to CR.

Additional Comments

Great thanks are owed to all assisting research colleagues, fishermen and the staff from Beqa Adventure Divers in Fiji. We authors thank Dr. Will White (CSIRO) for the bull shark tissue samples from Papua New Guinea via collaboration with a PNG-NFA ACIAR study, and the observers from commercial fishing vessels and artisanal surveys who collected the samples. We thank Crispen Wilson and Les Noble for sharing samples collected in South Africa and Indonesia. KG thanks the Ausbildungs-Stiftung fuer den Kanton Schwyz und die Bezirke See und Gaster (Kanton St. Gallen), the Shark Foundation Switzerland and Pacific Scholarship for Excellence in Research & Innovation of The University of the South Pacific. We thank Mike Neumann and Ian Campbell for continued advice during the study.

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Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.



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