Genetic segregation of great whites

For an animal that – to our current knowledge – shows no parental care, a surprising family drama is unfolding in the world of sharks. Perhaps the most iconic of species, new research shows that the great white shark (Carcharodon carcharias) is not the single global entity we once believed. Instead, it’s a tale of three long-lost cousins, and each lineage faces its own struggle for survival.

The ground-breaking study published in Current Biology has found that wild carnivores actually fall into three distinct genetic lineages that rarely mix when it comes to producing offspring. Using advanced genomic techniques, researchers at the University of Aberdeen in collaboration with an international team analyzed DNA from 89 great white sharks caught across their wide range (including from the Mediterranean to Australia). What they discovered was a species separated by ancient events and contemporary ocean currents, explains Dr. Catherine Jones, lead researcher from the University of Aberdeen: “At the end of the Penultimate Ice Age – between 100,000 and 200,000 years ago – great white shark populations appear to have split into three distinct lineages, which rarely interbreed.

This ancient separation, she says, has continued to the present day, with modern ocean currents serving as barriers that prevent these lines from mixing. Today, bloodlines are found in the North Atlantic and Mediterranean, North Pacific and South Indo-Pacific. “Successful conservation requires recognition of management units, but this has been unavailable for great white sharks, which were thought to exist as a single global population,” says Professor Les Noble of Nord University in Norway, who also holds a honorary position at the University of Aberdeen. The study only identified a single shark that appeared to be a hybrid between the two lineages, suggesting that while some interbreeding may occur, it is extremely rare. This genetic isolation means that if a population were to disappear, it could not be replenished by sharks from other regions.

Great white sharks are now classified as vulnerable on the IUCN Red List of Threatened Species, with global populations declining in recent decades. With this latest release, we now realize that every regional population is even more vulnerable than previously thought. “It has long been considered that sharks lost from one area will be compensated by the movement and mating of sharks from other locations. Our findings suggest that this is clearly unlikely and this, together with overfishing, depletion of their food reserves, pollution and poaching, could put this iconic apex predator at real risk of extinction,” Jones points out.

Their fearsome reputation often masks their vulnerability. Although sharks outlasted dinosaurs and countless other ancient animals, these magnificent predators may be swimming toward the end of their evolutionary path. The triple threat of genetic isolation, human activity and climate change may be too much. “The lack of interbreeding suggests that offspring from cross-line matings may not be viable,” explains Nord University Professor Galice Hoarau, who warns of a possible “genetic trap” on the horizon. “If recent predictions of changes in the strength and direction of major ocean currents over the next 50 years are correct, splitting these geographic boundaries between lines could allow for more unproductive matings, further endangering great white shark populations and diversity , the health and productivity of ocean ecosystems. .

The team agrees that although genomics is often neglected in assessments of biodiversity and conservation efforts, “the clear resolution it provides can help focus future scientifically informed global management decisions for the great white shark.” It may not be too late to protect not just one iconic animal… but three. (Well, sort of.)