Great white sharks are fascinating but mysterious creatures. Research on their DNA over the last two decades has uncovered surprising information that continues to puzzle scientists.
In 2024, a study revealed that great white sharks are not just a single global species. Instead, scientists found three distinct lineages, all traced back to a common group that lived about 10,000 years ago. This happened during the last ice age, which significantly reduced their numbers. The modern groups are now located in the northern Pacific, southern Pacific and Indian Ocean, and the northern Atlantic and Mediterranean.
Despite extensive research, the reasons behind these different groups remain unclear. Gavin Naylor, the director of the Florida Program for Shark Research, stated, “The honest scientific answer is we have no idea.” The similarities in nuclear DNA among these groups confound researchers, while their mitochondrial DNA shows significant differences. Mitochondrial DNA, which is inherited from the mother, has been a useful tool for conservation biologists to track populations and migration patterns, but it hasn’t worked as expected for great whites.
Scientists had once thought that female sharks return to their birthplace to reproduce, a concept known as female philopatry. Observational data suggested that while both male and female sharks travel far, females often return home to mate. However, when researchers tested this idea, they found no evidence supporting it. Testing 150 sharks worldwide revealed that the expected signals in their nuclear DNA were absent.
Other hypotheses, including the possibility of skewed sex ratios or random genetic changes known as genetic drift, also failed to explain the observed differences in DNA. Naylor proposed that if only a few females contribute to future generations, that could account for the disparities, but this too fell short of clarification.
Current theories suggest that an unknown evolutionary mechanism might be at work. Since there are only about 20,000 great white sharks globally, some speculate that natural selection could be honing their mitochondrial DNA to fit different environmental pressures. Yet, this remains highly doubtful without further evidence.
The researchers behind the study noted that their findings might also apply to other shark species previously thought to exhibit female philopatry based on genetic data. Understanding these mechanisms better could reshape our knowledge of shark populations in general.
This research sheds light on the complexity of evolution and the intricate web of life that great white sharks belong to. More studies are crucial for unraveling these mysteries and enhancing our conservation efforts for these incredible animals.
For more insights on this topic, you can read the study published in PNAS here.
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