The great white shark continues to give science headaches: while its Nuclear DNA is very homogeneous On a global scale, the genetic material they inherit from their mother shows marked differences. In parallel, the tagging of a large specimen off the east coast of the United States allows us to observe in real time how this superpredator moves.
Two sources of information converge on the species: on the one hand, research published in PNAS confirms three major genetic groups; on the other hand, Ocearch has instrumented an individual of unusual size with a tag that will offer movement data for yearsTogether they paint a finer—and at the same time more enigmatic—picture of the great white.
A colossus marked in the US: what we know about Contender
The Ocearch team has captured, measured and released a great white shark nicknamed Contender that reaches 4,2 meters long and around 750 kilos, figures that place it as the largest scored by the organization to date.
To track it accurately, a tag was installed on it SPOT, a device that transmits positions when the animal raises its dorsal fin. This technology can provide real-time metrics for about five years and is key to understanding the routes, rhythms and seasonality of their movements.
Since his marking in winter, records show that Contender has performed almost 500 kilometers travel. Among the latest verified signs are areas such as Merritt Island (Florida) and crossings through Outer Banks (North Carolina), a common migratory corridor for the species.
The genetic map that divides the great white shark into three lineages
The research signed by an international consortium - among them specialists such as Romuald Laso-Jadart, Shannon L. Corrigan and Gavin J.P. Naylor— integrated complete genome sequencing, targeted gene capture and demographic simulations with samples of 150 great white sharks coming from various points on the planet.
The team assembled a high-quality reference genome from a juvenile from California: about 4.286 billion base pairs with a percentage of repeats close to 61,7%The remaining data were aligned on this framework to explore structure and connectivity.
The analyses resolve three autosomal lineages with defined geographic distribution: North Pacific; Indo-Western Pacific + South Pacific; and North Atlantic + Mediterranean. That is, separate populations, but with a certain recent patency between them.
By incorporating recent migration, the models improve their likelihood, suggesting that the separation between lineages is relatively young and does not exclude gene exchanges – even between the Mediterranean and the North Atlantic.
Why mitochondrial DNA doesn't match nuclear DNA
The great puzzle is the discordance between a Very similar nuclear DNA in different regions and a mitochondrial DNA with obvious differences. The classical hypothesis attributed this disparity to the female philopatry, where females return to their natal area to reproduce, preserving more isolated maternal lineages.
After analyzing it with multiple scenarios—without philopatry, with extreme female philopatry, and with male philopatry—the models suggest that the natal fidelity of females resembles the observed pattern, although it does not fully explain it. To adjust the mitochondrial haplotype distribution, it was necessary to assume higher mutation rates in the mitochondria.
Other hypotheses, such as a skewed sex ratio or random genetic drift, also fail to resolve this enigma. The authors propose that there must be some additional evolutionary mechanism which has not yet been clearly identified.
With an estimated world population of around 20.000 copies, the species combines rarity, high mobility and long life cycles, which complicates statistical studies. Therefore, the integration of genomics, labeling and modeling is crucial to better understand its biology.
From these findings, a predator is observed with three main lineages connected at different moments in time, and with maternal inheritances that do not entirely coincide with that history. The monitoring of specimens like Contender offers valuable clues to protect critical routes and habitats, in an effort to understand and conserve this enigmatic species.
