Cosmopolitan marine pelagic species display variable patterns of population connectivity among the world’s major oceans. While this information is crucial for informing management, information is lacking for many ecologically important species, including apex predators. In this study we examine patterns of genetic structure in the broadnose sevengill shark, Notorynchus cepedianus across its global distribution. We estimate patterns of connectivity among broadnose sevengill shark populations from three major oceanic regions (South Atlantic, Oceania and Eastern Pacific) by contrasting mitochondrial and nuclear DNA haplotype frequencies. We also produced time calibrated Bayesian Inference phylogenetic reconstructions to analyses global phylogeographic patterns and estimate divergence times among distinctive shark lineages. Our results demonstrate significant genetic differentiation among oceanic regions (ΦST = 0.9789, P < 0.0001) and a lack of genetic structuring within regions (ΦST = − 0.007; P = 0.479). Time calibrated Bayesian Inference phylogenetic reconstructions indicate that the observed patterns of genetic structure among oceanic regions are historical, with regional populations estimated to have diverged from a common ancestor during the early to mid-Pleistocene. Our results indicate significant genetic structuring and a lack of gene flow among broadnose sevengill shark populations from the South Atlantic, Oceania and Eastern Pacific regions. Evidence of deep lineage divergences coinciding with the early to mid-Pleistocene suggests historical glacial cycling has contributed to the vicariant divergence of broadnose sevengill shark populations from different ocean basins. These finding will help inform global management of broadnose sevengill shark populations, and provides new insights into historical and contemporary evolutionary processes shaping populations of this ecologically important apex predator.
Bibliographical noteFunding Information:
Mahmood S. Shivji and Christine C. Bruels were funded by the Save Our Seas Foundation, Guy Harvey Ocean Foundation, and Hai Stiftung/Shark Foundation. Adam Barnett secured funding from Sea World Research and Rescue Foundation Inc., Save Our Seas Foundation, Holsworth Wildlife Fund, Winnifred Violet Scott Trust, and National Geographic.
We thank P. Scott, Shark Dive NZ , DAFF and the RV Ellen Khuzwayo staff in South Africa for tissue collection. ASR thanks Prof. Jayson Semmens from the University of Tasmania for his PhD supervision and Prof. Gabriele Gerlach for her support and hospitality at the Carl von Ossietzky Universit?t Oldenburg. We would also like to thank the two anonymous reviewers for their constructive comments, which helped to improve the manuscript.
© 2021, The Author(s), under exclusive licence to Springer Nature Switzerland AG.
- Global distribution
- Population structure patterns
- Species management