The genetic makeup of sharks changes much more slowly than that of other vertebrates. The rate of change in epaulette sharks in particular is only about a twentieth of the rate in humans, as researchers led by Manfred Schartl from the University of Würzburg report in the journal “Nature Communications”. This is the lowest mutation rate ever known in vertebrates.
This has advantages and disadvantages for the fish living off Australia, as the research team explains: The fact that changes so rarely occur in the animals’ genetic makeup is a possible explanation for their exceptionally low risk of cancer. However, they may adapt to environmental changes more slowly than other animals for the same reason.
Genetic changes are the basis for evolution: Some bring a survival advantage to the affected animals and are therefore more likely to be preserved because these specimens have a greater chance of producing more offspring. But the disease cancer is also based on spontaneous small changes in the DNA, which lead to malfunctions of the affected cells and unbridled cell proliferation.
A low mutation rate could also be a disadvantage
The low mutation rate can be a disadvantage for sharks, especially if their population is already significantly reduced and they then have to adapt to a rapidly changing environment, as the researchers explain. For the study, the team from Germany, Australia, Sweden and the USA compared the genomes of one pair of parents with the genomes of nine offspring, recorded the genetic differences and thus determined the mutation rate.
Sharks are very old in terms of evolutionary history. They have populated the world’s oceans for around 400 to 500 million years, and their basic appearance has hardly changed during this enormous period of time. Sharks reach sexual maturity late, have a slow metabolism, live very old and have few offspring. Overfishing, habitat loss and climate change are causing declines in the populations of many shark species.
Epaulette sharks (Hemiscyllium ocellatum) live in coral reefs down to 60 meters depth. They only grow a little larger than one meter, are mostly out at night and rarely swim. Instead, they use their fins as feet and “walk” across the ocean floor.
Epaulette sharks are limited to warm tropical waters, while even lower mutation rates could be expected in shark species in cold waters with even lower metabolic rates, the scientists explain. A possible example is the Greenland shark (Somniosus microcephalus), which can live around 400 years.
