DNA Differences in Great White Sharks Have Instigated an Unsolved Mystery
A genetic mystery in white sharks (Formerly large white sharks) has been perplexed for scientists for over 20 years. Between three large populations of sharks, the differences in mitochondrial DNA raised the eyebrows. While migration models initially emerged as an appropriate response, a new study has canceled this common theory.
THE studypublished in Proceedings of the National Academy of Sciencesrevealed that this long -term mystery is from the end of the last glacial age 10,000 years ago. Over time, a population of white sharks was divided into three distinct populations which each presented a genetic variation. Several theories to explain DNA differences have missed the brand so far, but scientists are not over to seek answers.
The mystery of the white shark
Before the end of the last glacial period 10,000 years ago, white sharks lived in a single population of the Indo-Pacific Ocean due to the low level of the sea. However, when the earth started to warm up, they migrated to other parts of the world, preparing them the way to diverge genetically about 7,000 years ago.
Today, three populations with distinct genetic features exist: one in the southern hemisphere near Australia and South Africa, one in the Northern Atlantic and one in the North Pacific. The overall figures of white Sharks are however very low.
“There are probably around 20,000 people on a global scale,” said the co-author of the study Gavin Naylor, director of the Florida program for shark research at Florida Museum of Natural History, in a statement. “There are more fruit flies in a given city than large white sharks worldwide.”
In 2001, a study came to something unexpected in the DNA of white sharks. Based on genetic samples of sharks in Australia, New Zealand and South Africa, the researchers found that DNA in the nuclei of their cells was mainly the same between individuals, but DNA in the mitochondria of South African sharks was different from those of Australia and New Zealand.
The researchers originally thought that the isolation of the groups would have allowed everyone to develop their own differences in mitochondrial DNA. But that did not explain why their nuclear DNA was almost identical.
Learn more:: Great White Sharks regroups to tackle whales
A common demystified theory
An emerging theory said that differences in mitochondrial DNA were born from the trend of female sharks not to travel far and always go home for the reproduction season (behavior called philopatria), while men have traveled great distances. It is important to note that female sharks are also generally those that give their mitochondria to the next generation.
According to this theory, nuclear DNA has remained similar among the populations because men would come out and mix with the sharks in other populations. The differences in mitochondrial DNA, on the other hand, were attributed to women who generally return to the same place to reproduce.
However, the new study discovered that migration could not be the answer. The researchers conducted a study similar to that of 2001, analyzing DNA from different shark populations. They carried out tests to determine the validity of the theory of Philopatria, but the results of DNA showed that he was not really responsible for the mitochondrial schism between the populations.
An unresolved case
Currently, researchers find themselves with a potential explanation: natural selection. But even it seems to be an improbable response. Indeed, natural selection promotes larger populations to transmit features favorable to offspring, while the genetic drift often leaves smaller populations with an increased chance of transmitting random lines which can sometimes be unfavorable.
The results of the study have confirmed that the genetic drift cannot explain the differences in mitochondrial DNA because it is a random process which does not target a particular type of DNA while saving another.
The only remaining explanation is natural selection, although Naylor says that due to the size of small populations in white sharks, this process “should be brutally fatal”. By that, it means that “deviation from the most frequent mitochondrial DNA sequence in a given population would probably be fatal, thus ensuring that it has not been transmitted to the next generation”, according to the press release.
The researchers note that it is far from being a final conclusion and that other studies are necessary to validate natural selection as possible explanation. For the moment, the mystery of the DNA of Great White Sharks lives.
Find out more: “Super” can be started with this name, but these 10 facts of white shark are quite killer
Article Sources
Our writers at Discovermagazine.com Use studies evaluated by high -quality peers and sources for our articles, and our publishers examine scientific precision and editorial standards. Review the sources used below for this article:
Jack Knudson is a deputy editor -in -chief to discover with a strong interest in environmental sciences and history. Before joining Discover in 2023, he studied journalism at the Ohio University Scripps College of Communication and previously interned at recycling Today Magazine
