The great white shark has survived for millions of years, outlasting the dinosaurs and countless other species. But now, faced with the triple threat of genetic isolation, human activity, and a changing climate, these magnificent predators may be swimming towards an evolutionary dead end. The question remains: will we act in time to protect not just one species, but three unique lineages of ocean guardians?

The researchers used two main genetic approaches in this study. First, they performed "target gene capture" on all 89 shark samples. This technique allows scientists to selectively sequence specific parts of the genome that are likely to show variation between individuals.

They then performed more extensive "whole genome sequencing" on a subset of 17 sharks representing different geographic areas. This provides a more complete picture of genetic variation across the entire genome. By combining these approaches, the team could identify genetic differences between sharks from different regions with high accuracy.

The genetic analysis revealed three distinct clusters of white sharks, corresponding to different ocean regions. These clusters showed very little genetic mixing, suggesting they rarely interbreed. The only exception was a single shark that appeared to be a hybrid between two lineages. Statistical analyses estimated that these lineages diverged between 100,000-200,000 years ago. The study also found some evidence of finer-scale genetic structure within each main lineage, suggesting there may be even more localized populations.

While this study provides strong evidence for distinct white shark lineages, there are some limitations to consider. The sample size, while substantial for such a rare and difficult-to-study species, is still relatively small. More extensive sampling could potentially reveal additional genetic complexity. Additionally, genetic data alone cannot fully explain the mechanisms keeping these lineages separate - further research on shark behavior and ecology is needed to understand why interbreeding is so rare.

This study challenges our understanding of white shark population structure and has major implications for conservation. The existence of distinct lineages means that losing any one population would result in a significant loss of genetic diversity for the species as a whole.

The research also suggests that white sharks may have more limited dispersal than previously thought, making them potentially more vulnerable to localized threats. The authors argue for a shift in conservation strategy, treating each lineage as a separate management unit. They also highlight the need for further research to understand the ecological and behavioral factors maintaining this genetic separation.

This project was funded by Nord University, Faculty of Biosciences and Aquaculture, Norway. Some DNA sequencing was performed by the Norwegian Sequencing Centre, which is supported by the Research Council of Norway and the South-Eastern Norway Regional Health Authorities. The authors declared no competing interests related to this research.