The primitive-looking coelacanth has long been considered a ‘living fossil’, with existing specimens very similar to fossils dating from the Cretaceous. But while the coelacanth’s body may have changed little, its genome tells a different story.
Latimeria chalumnae to Pumula on the KwaZulu-Natal South Coast, South Africa, on 22 November 2019. Image credit: Bruce Henderson, doi: 10.17159 / sajs.2020 / 7806.
Coelacanths are fish fish with lobe fins that presumably became extinct for 65 million years until a first living specimen was discovered by chance in South Africa in 1938 by a South African museum curator on a local fishing trawler.
There are two types of coelacanths that exist: Latimeria chalumnae forms the Comoros Islands off the east coast of Africa, and Latimeria menadoensis from the waters along Sulawesi, Indonesia.
Selakante offers several unique and intriguing features such as unpaired fins that look like linked fins and strongly modified lungs / swim bladder.
Along with lungfish, they are the closest relative of tetrapods and share their morpho-anatomical features with them that are not found in vertebrates that are far away such as jet fins.
When the first existing coelacanth was discovered, it is reminiscent of so many fossil forms from the Cretaceous that it was designated a ‘living fossil’, that is, a species with a morphology that did not develop much over a long period of time.
To offset these morphological stasis, coelacanths have often been suggested to have a slow or even non-evolving genome.
“Coelacanths may have evolved a little slower, but they are certainly not a fossil,” says Isaac Yellan, a graduate student in the Department of Molecular Genetics at the University of Toronto.
In their new study, Yellan and colleagues found this Latimeria chalumnae 62 new genes obtained through encounters with other species 10 million years ago.
What is even more fascinating is how these genes originated. Their sequences indicate that they originated from transposons, also known as ‘selfish genes’.
These are parasitic DNA elements whose sole purpose is to make more copies of themselves, which they sometimes achieve by moving between species.
“Our findings are a striking example of this phenomenon of transposition that contributes to the genome of the host,” said Professor Tim Hughes, a researcher at the Donnelly Center for Cellular and Biomolecular Research at the University of Toronto.
“We do not know what these 62 genes do, but many of them encode DNA-binding proteins and probably play a role in gene regulation, where even subtle changes are important in evolution.”
The findings were published in the journal Molecular biology and evolution.
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Isaac Yellan et al. Various eukaryotic CGG-binding proteins produced by independent households of hat transponders. Molecular biology and evolution, published online on February 9, 2021; doi: 10.1093 / molbev / msab007