Great white sharks have been in Mediterranean for 3.2M years

White sharks have been living in the waters of the Mediterranean for much longer than previously estimated.

According to a study published this week in the Journal of Biogeography, the apex predators have been living in the Mediterranean for 3.2 million years.

To trace their evolutionary origins, researchers at the University of Bologna used mathematical models to analyze the DNA of Mediterranean white sharks, which share more genes with their Pacific peers than their neighbors in the Atlantic.

"White sharks have a complex evolutionary history, they are unusual," Agostino Leone, researcher at the University of Bologna, said in a news release. "They evolved into sedentary populations scattered around the globe."

"Among these, there are the Mare Nostrum white sharks, which are really unique," said Leone. "White sharks in the Mediterranean have a very low genetic variability, which may hint at a very small and endangered group of sharks."

Few predators have captured the imagination of humans like the great white shark, and yet, scientists know relatively little about their evolutionary history.

The great white shark, Carcharodon carcharias, can grow up to 20 feet in length, making it the largest predatory fish on Earth. They're found in all the world's major oceans, as well as the Mediterranean.

But whereas white sharks in other parts of the world have seen their numbers rebound in recent years, the population of white sharks endemic to the Mediterranean is shrinking, making them harder for scientists to study.

Thanks to advances in genomic analysis methods, researchers were able to sequence and study the mitochondrial DNA of Mediterranean white sharks.

"This new data allowed us to observe the biological diversity of white sharks living in the Mediterranean," said Leone. "By analyzing and comparing different specimens, we were able to estimate that the white shark population in the Mediterranean started to evolve differently from other cognate populations around 3.2 million years ago. This essentially proves that those theories about sharks colonizing the Mediterranean around 450,000 years ago are wrong."

The analysis performed by Leone and his colleagues suggests the Mediterranean white shark is not only older than scientists thought, but that the population likely split off from white sharks living in the Pacific. Scientists estimate the sharks trekked from the Pacific to the Mediterranean, crossing the Atlantic, before the Isthmus of Panama that now separates North and South America had formed.

Scientists suspect the Atlantic was populated by white sharks much later, perhaps by white shark populations off the coast of southern Africa.

In addition to revealing the Mediterranean white shark's evolutionary origins, the latest analysis showed the genetic diversity among white sharks in the Mediterranean is dwindling. Previous research suggests isolation and human activities such as over-fishing can negatively affect genetic diversity. A lack of genetic diversity can cause harmful genetic mutations to accumulate in local populations.

Authors of the new study suggest their findings support the Mediterranean shark being designated as endangered.

"The Mediterranean population of white sharks is probably a small endangered community," said Leone. "To save them, it is fundamental to act quickly: Their extinction would be detrimental to the ecological balance of the Mediterranean Sea as well as to the already highly unstable global situation of these majestic sea predators."

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Biologists publish first global map of fish genetic diversity
Washington DC (UPI) Feb 10, 2020
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