Unraveling the Mystery: New Revelations About Great White Sharks Leave Scientists Stunned!

Great white sharks are fascinating and often misunderstood. Despite being famous worldwide, we still have much to learn about them. A recent study has uncovered an intriguing mystery about their genetics that leaves scientists puzzled.

Researchers have noticed significant differences between the nuclear DNA and mitochondrial DNA in great white sharks. While these differences were previously attributed to their migration patterns, a new study challenges that idea by examining genetic variations across global shark populations.

To understand the background, we have to look back about 10,000 years. At that time, during the last ice age, sea levels were much lower. This limited the great white shark population, which shrank to just one mixed group in the southern Indo-Pacific Ocean. According to Gavin Naylor, director of the Florida Program for Shark Research, this was a critical period. Glaciers locked away water, causing sea levels to plunge to about 40 meters (131 feet), which led to a dramatic decline in their numbers.

Once the ice melted, sea levels rose, and sharks began to spread out. Around 7,000 years ago, they started to genetically diverge, leading to three distinct populations: one in the southern hemisphere, one in the northern Atlantic, and one in the northern Pacific. Despite this wide distribution, their overall numbers remain worryingly low. Naylor estimates there are only about 20,000 great white sharks worldwide. To put that in perspective, there are more fruit flies in a single city than there are great whites globally.

The mystery deepens when we look at the study’s findings. Earlier research from 2001 found that while the nuclear DNA of sharks from different regions was similar, the mitochondrial DNA from South African sharks was quite distinct. This raised questions: why the discrepancy? Scientists hypothesized that female sharks, which tend to return to the same areas to breed, contributed to these genetic differences. However, this idea has never been rigorously tested due to the challenge of obtaining DNA samples from these elusive predators.

Naylor has been working on gathering shark DNA for over 13 years. He aimed to establish a nuclear genome for further study. By sequencing mitochondrial genomes from around 150 sharks, he confirmed earlier findings: sharks in the North Atlantic rarely mixed with those in the South Atlantic, and similar patterns were found in the Pacific and Indian Oceans.

Still, the hypothesis about female philopatry—where females return to their birthplaces to mate—was not supported by nuclear data from this study. When the researchers examined evolutionary history, they found the once-narrow population expanded after the last ice age and settled in northern waters where food was abundant, likely seal populations.

The study also considered genetic drift, a concept suggesting that small populations can carry random mutations more easily. However, such changes would not explain the specific discrepancies in mitochondrial DNA. As Naylor points out, natural selection would have to be very strong to produce these differences, which seems unlikely given the sharks’ small numbers.

The conclusion? We still have no clear answers, and the mystery surrounding the genetics of great white sharks invites further exploration. As research continues, we may uncover more about these remarkable ocean dwellers.

For more details, check the study published in PNAS.



Source link