Once-Believed Extinct, 'Living Fossils' Fish Shows its True Color on New Study

A study of coelacanth DNA indicates that its genome has undergone several major changes in recent evolutionary history, possibly dispelling the common picture of these legendary fish as' living fossils.' However, this might not be as black and white as it seems.

The discovery in 1938 of a living coelacanth of South Africa's coast was quite a shock, as it was thought that these species were extinct. Thanks to their eerie similarity to near-identical creatures spotted in the fossil record, the big fish were eventually referred to as' living fossils.'

A recent study published in Molecular Biology and Evolution reveals that at least one genus of the coelacanth, formally referred to as Latimeria chalumnae, is not the living fossil it is thought to be, having gained hundreds of new genes over the past 23 million years, a startling discovery and a far cry from the belief that the species has hardly evolved since its ancestors appeared over 300 mi Moreover, the discovery is further confirmation that the idea of living fossils is obsolete and something of a misnomer.

Isaac Yellan, the first author of the new study, explained in an email that not much is known about coelacanths, but they are not especially aggressive, and they're still very social. L. Yellan, a graduate student with the Department of Molecular Genetics at the University of Toronto, said that the chalumnae live in the Indian Ocean and the waters off the coast of southeast Africa and, while not extinct, the fish are elusive and critically endangered.

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Transposon

When researching proteins that bind DNA, Yellan and his colleagues made the discovery with an emphasis on a protein called CGG Binding Protein 1 (CGGBP1).

The function of this protein in humans has been studied by other scholars. Still, its role in evolutionary history is poorly known, as is its obvious resemblance to a particular family of transposons, DNA sequences capable of changing locations within a genome.

This prompted the team to research binding proteins on a quest that ultimately led them to the idiosyncratic fish in other animals.

"The African coelacanth came into the picture when we started looking for CGGBPs [DNA binding proteins) in published genomes, and found out that it has 62 CGGBP genes-way more than any other vertebrate," explained Yellan. "We then started to look into where this large gene family might have come from."

According to the article, the researchers aren't entirely sure what these 62 transposons are doing, but they're presumably playing a part in gene control.

Coelacanth Genome

Yellan and his collaborators, including University of Toronto molecular geneticist Tim Hughes, identified similar genes in other animals' genomes. Still, the spread of these genes suggested that they evolved outside of common ancestors.

Indeed, through interactions with other species, including distantly related species, some but not all transposons are acquired in a process known as horizontal gene transfer.

The authors do not establish the exact origin of the L-documented transposons. Chalumnae, but there are specific suggestions they have.

"One way that transposons can be picked up and carried between species is through a parasitic intermediary host, such as a lamprey, which feeds on the blood of fish," said Yellan. "This is supported by the fact that we found one of these transposons in a lamprey species, although we don't know if coelacanths received it from the lamprey, or vice-versa."

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