Surprising creature that can 'interbreed across 100 million years of evolution'

Researchers discovered that fish - a species known as a "living fossil" - has the slowest evolutionary rate of all vertebrates and jawed animals.

Snakehead fish are living fossils that have changed at an extremely slow rate since their ancestors appeared during the time of the dinosaurs 150 million years ago, according to research published in the journal Evolution. That rate of change means this prehistoric fish evolved the slowest at the molecular level among vertebrates and jawed animals, Live Science reported on March 13.

The lineage of lepisosteidae (family Lepisosteidae) has existed for millennia, with the most anatomically modern species remaining in the fossil record from the late Jurassic period (145 - 163.5 million years ago). The 7 species alive today are distributed in rivers and lakes of North America and South America, one species sometimes lives in marine environments. In the new study, scientists examined catfish and many other long-term stable species.

The fish has remained almost unchanged since prehistoric times. (Photo: Newsweek).

Although many species closely resemble their fossil relatives, they have actually undergone evolutionary changes, although they may not be obvious. To become a living fossil, an organism needs to share an ancient ancestor with an extinct lineage, change minimally in appearance from its fossil relatives, and differentiate into a small group of related species. according to research team leader Chase Brownstein at Yale University.

Researchers use computer analysis to look at gene sequences from common ancestors called homologous genes, helping to reveal the rate of gene replacement or mutation over time. When a mutation repairs or changes a DNA sequence, it becomes a gene replacement, Brownstein explains.

The study found that some animals considered living fossils such as the tuyatara (Sphenodon punctatus), the coelacanth (Latimeria chalumnae) and the wild-hoofed chicken (Opisthocomus hoazin) differ significantly from their fossil relatives, although they retain many of their characteristics. Among the 471 species surveyed, catfish and sturgeon had the slowest rate of gene replacement. Sandfish appear to evolve at a rate three times slower than any other vertebrate alive on Earth.

Gene replacement leads to changes in shape. Therefore, the slow rate of gene replacement in this group of fish corresponds to the slow rate of species formation, meaning their lineage does not differentiate into many new species that are different in appearance like other groups. Instead, the few species that appear remain stable over long periods of time.

Catfish evolve so slowly that two species separated by 100 million years of evolution can still interbreed. The North American giant spatula (Atractosteus spatula) hybridizes with the rocket alligator (Lepisosteus osseus) in rivers in Texas and Oklahoma. What's even more strange is that their hybrids are able to reproduce. Artificial and natural hybrids are sometimes infertile, even when closely related, as is the case with the mule, a cross between a horse (E. caballus) and a donkey (E. asinus). In particular, the North American giant shark and the rocket crocodile have not crossed much throughout their evolutionary history, despite sharing the same habitat for about 55 million years. Crossbreeding may occur because the two species are forced to share spawning areas in some riverine mudflats.

According to Brownstein, the study raises the question of how the genomes of catfish and other living fossil species remain so stable.