Scientists have discovered that great white sharks split into three distinct populations about 100,000 to 200,000 years ago and never interbred again – except for one hybrid found in the Bermuda Triangle.
The study, published in Current Biology, analyzed the genomes of 89 great white sharks from around the world. The results showed that the sharks were segregated into three groups that diverged over time and did not interbreed. These groups are found in different locations: the North Atlantic/Mediterranean, Indo-Pacific, and North Pacific oceans.
The study’s findings suggest that if one of these populations goes extinct, it cannot be replaced. This has implications for conservation efforts. “Now we understand that if you wipe out sharks in a particular area, they’re not going to be repopulated by sharks from another lineage,” said Leslie Noble, a molecular evolutionary ecologist at Nord University.
The researchers used mitochondrial DNA, which is passed down only through the mother’s line, to study the genetic diversity of the sharks. However, this type of DNA can be prone to mutation, making it unreliable for tracing the lineage divergence.
To overcome this issue, the team analyzed variations of white shark DNA at a single nucleotide level – its basic building block. They found that the sharks were segregated into three distinct populations.
The study’s findings also suggest that the drop in sea levels and changes in ocean currents and temperature may have created a biogeographical barrier for these sharks.
One interesting discovery was the presence of a hybrid shark, a mix of the Indo-Pacific and North Pacific lineage, found in the Bermuda Triangle. It is possible that more instances of interbreeding have occurred but that the offspring of these hybrids were lost through natural selection.
The International Union of Conservation of Nature (IUCN) considers the great white shark vulnerable to extinction. These sharks lost about a third of their population between 1970 and 2018, but thanks to global protection efforts, their populations are slowly increasing.
Conservation efforts should focus on maintaining each unit of the white shark population, as interbreeding could occur and produce offspring that may not survive. The disappearance of these apex predators would also have huge implications for humans, as they play a crucial role in keeping marine ecosystems healthy.
Source: https://www.livescience.com/animals/sharks/great-white-sharks-split-into-3-populations-200000-years-ago-and-never-mixed-again-except-for-one-hybrid-found-in-the-bermuda-triangle