This “living fossil” fish continues its evolution despite its archaic appearance

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The coelacanth is a genus of mythical fish that is wrongly considered to be a “living fossil”. Despite the fact that these fish appeared during the Devonian around 350 million years ago, they have indeed very little morphologically evolved until today. Yet researchers have recently identified several new genes in their genome.

Discovery of 62 new genes in this fish

Coelacanths (or coelacanthiformes) are an order of sarcopterygian fishes (vertebrates with fleshy limbs). Having made their appearance during the geological era of the Devonian, these fish have physically changed little since. The first living specimen, an African coelacanth (Latimeria chalumnae), was fished in 1938. Now, this one strongly resembled known fossils dating from the Triassic period, around 250 million years ago. The rather archaic appearance of coelacanths means that they are mistakenly considered to be “living fossils”, which implies that these fish have not evolved for millions of years. However, this is false, since their genome has evolved well.

In a study published in the journal Molecular biology an evolution on February 9, 2021, researchers from the University of Toronto (Canada) focused on the African coelacanth. This work enabled the discovery of 62 new genes in its genetic heritage. If the function of these genes is still unknown, scientists believe they have understood how the coelacanths acquired them.

Credit: MarineBio

The “jumping genes” at the origin of these genes

It should be noted that the genome of the coelacanth consists of approximately 25% of transposable elements (let’s transpose). These are fragments of DNA known as “jumping genes”, capable of separating from the base sequence in order to integrate into another. An enzyme called transposase then allows the transposon to perform this operation. These mobile elements attach to DNA over time and can be at the origin of new genes that can allow an evolution of the genome. According to scientists, the 62 new genes in question of the African coelacanth come from transposons that enriched its genetic heritage nearly ten million years ago.

The researchers analyzed the sequence of these genes and believe that they code for proteins playing a role in the regulation of gene activity. They could, for example, be DNA binding proteins or else transcription factors. Rather discreet, these genes can be very important for the coelacanth to adapt to its environment. So if these genes did not change the appearance of the fish, they nevertheless bear witness to its evolution.

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