Sharks have been sailing our oceans for millions of years (they appeared before trees). The Earth and its inhabitants have undergone tremendous changes, but sharks have remained remarkably consistent, both in their biology and in the shape of their bodies. This unchanging nature has long fascinated scientists, but a groundbreaking international research initiative involving experts from Germany, Australia, Sweden and the United States has revealed the extraordinary mystery behind the shark’s enduring legacy.
Led and coordinated by the research team led by Senior Professor Manfred Schartl from the Department of Developmental Biochemistry at the University of Würzburg, this groundbreaking study, published this week in the renowned journal Nature Communications, sheds light on the genetic stability of sharks and their future-reaching future Implications.
For this scientific project, researchers ventured to the northeast coast of Australia to catch bullhead sharks. The great bullhead shark (Hemiscyllium ocellatum) is a small species of shark in the family Hemiscylliidae. These creatures, most commonly known as the “walking shark,” exhibit a unique style of movement that resembles walking on the ocean floor, hence their name.
They are commonly found in the western Pacific, particularly in the waters off the coasts of Australia and Papua New Guinea, where they live in shallow coral reefs and on sandy and rocky seabeds. They are primarily nocturnal, feeding on small invertebrates such as crustaceans and small fish at night and retreating to coral reef crevices and caves during the day.
Once in Australia, the team set up a breeding station at the Australian Regenerative Medicine Institute (ARMI) at Monash University. A group of breeding bullhead sharks were maintained in a closed marine circulation system and were originally obtained as adults from various locations in Queensland. Blood samples were taken and a particular breeding pair were placed in a specially made tank so that eggs of known parentage could be collected. These eggs were marked, transferred to separate aquariums and raised until the final hatching stage before it is preserved for DNA extraction. The research team first constructed a high-quality reference genome and then carefully sequenced the complete genomes of the shark relatives. This innovative device allowed scientists to genetically assess the mutation rate within a shark family tree for the first time.
The results are stunning: the estimated mutation rate is 7×10-10 per base pair per generation, the lowest ever measured in vertebrates. This mutation rate is ten to twenty times lower than in mammals. At first glance, this incredibly low mutation rate seems like good news, especially when it comes to cancer rates in sharks. “The low mutation rate could play a decisive role,” says Schartl. However, this genetic standstill is double-edged. Mutations play a critical role in improving genetic diversity within populations, enabling adaptation to changing environmental conditions and driving evolution. Due to the rapid development of sharks, there is a risk that they will have to contend with ecological pressures such as overfishing and loss of habitat. And that’s exactly what happens. Shark populations around the world have plummeted, and many of the approximately 530 known species are now threatened with extinction. Sharks play a crucial role in marine ecosystems, and their protection and preservation of their genetic diversity are crucial.
The low mutation rate observed in bullhead sharks can be attributed to various factors. One possible reason is their poikilothermic nature, which is characteristic of cold-blooded animals with a low metabolic rate. This property, combined with effective purifying selection within a species with a large long-term population size, allows the elimination of mildly deleterious mutations. This selection process could favor genes responsible for efficient DNA repair, as genes that ensure genome stability have shown signs of positive selection in Elasmobranchii (which includes sharks). “The extrapolation of our results to other shark species that lack the population size stability observed in bullhead sharks suggests that a similarly low mutation rate may have long-term negative effects on population bottlenecks in already threatened and overfished species,” the authors explain. “Our study therefore provides compelling evidence for the need to prioritize conserving the remaining genetic diversity of global shark populations. »
Article translated from Forbes US – Author: Melissa Cristina Márquez
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