This “living fossil” has remained virtually unchanged in 150 million years

The caiman has the slowest rate of molecular evolution of all jawed vertebrates. This tells us something not only about its evolution, but also about possible modifications in the future.

In the new research from Yale University Scientists have unlocked the genetic secrets of the Caiman Pike, an ancient group of ray-finned fish that has remained virtually unchanged for millions of years. The seven living species are structurally nearly identical to the oldest fossil caiman spears from the Jurassic Period, about 150 million years ago. The research shows that this is due to an extremely low mutation rate, up to 10 times lower than that of mammals. This means that their DNA changes less than that of other animals, causing their genes and proteins to evolve significantly more slowly.

This is remarkable. Mutations can be very beneficial to the survival of a species. While most mutations provide relatively few benefits, some changes can allow species to better adapt to their environment. Especially when living environments change. “We were surprised by how slowly the pike and caiman evolved at the molecular level,” says John Lundberg. This is confirmed by co-author Chase Brownstein. “This is a unique phenomenon among vertebrates. Living fossils such as the caiman spear show that some species can adapt over long periods of time with minimal genetic change.

DNA repairs
Researchers believe there is an explanation for this. In fact, caimans appear to be unusually good at repairing their own DNA, allowing them to correct somatic mutations and germline mutations (changes in DNA that occur before and after pregnancy) more efficiently than most other vertebrates. Since they also have a fairly long lifespan (they can live up to a hundred years), there is also plenty of time to repair DNA damage and remove mutations in their bodies.

This is not only good for them, but perhaps for us as well, says researcher Thomas Near. “Most cancers are mutations in the body that represent a failure of an individual's DNA repair mechanisms. If further research shows that caiman's DNA repair mechanisms are highly effective, and discovers what makes them so, we can begin to think about potential applications for human health.”

Hybrid offspring
The researchers also discovered that two species belong to the pike caiman family (Atractostius spoon And Lepisotheus Osius) separated by more than 100 million years of evolution still produce viable and fertile offspring. This makes it the oldest known mixture of all animals, plants and fungi that produce fertile and viable hybrids. Two species of fern that previously held the 60 million-year-old record have been defeated. So slow evolution also has advantages, as Brownstein explains: “The slower a species mutates, the more likely it is that it will be able to interbreed with a distinct species from which it has been genetically isolated for a long period of time.”

Living environment
A final explanation for the slow evolution is that the caiman had a very constant living environment all these years. They have lived in relatively stable freshwater habitats for millions of years, which means there is less pressure to adapt quickly. “These factors may have worked together to reduce the mutation rate in pike caimans and stabilize their genomes,” says Brownstein. “Which allowed them to survive for millions of years with little change.”

Therefore, the rate of evolution is far from equal between species. This insight affects not only our interpretation of fossil records, but also our expectations about how species will respond to future changes in their environment, such as those caused by climate change. “This research helps us understand the diversity of life on Earth and the factors that influence its evolution,” Lundberg said. “It is an important step forward in our knowledge of the history of life.”