Biologists have learned how seahorse relatives got their strange shape

(ORDO NEWS) — The so-called “sea dragons”, seahorses and their relatives from the needle family have a very bizarre shape and lifestyle.

In a new study, biologists turned their attention to their genome and figured out how these fish evolved.

Among the many strange and unusual sea creatures, fish from the needle family stand out. They are not at all like ordinary fish: either very thin and elongated (like sea needles), or curved and with a curved spine (seahorses and “sea dragons”, sea dragons).

It was on their example that scientists from the United States decided to figure out what changes in the genomes of fish made such a structure possible.

The objects of study were two “sea dragons” – Phyllopteryx taeniolatus and Phycodurus eques , also known as the rag-picker seahorse.

They are related to true seahorses ( Hippocampus sp. ) by their curved spine, thin elongated snout, which is devoid of teeth and is well suited for feeding on small marine life. As in the case of skates, males take care of the offspring of these fish.

However, the studied fish, perhaps, look even more outlandish – because of the numerous spikes and outgrowths on the body.

They look like seaweed and provide good camouflage against the background of underwater thickets, also due to the special swaying manner of movement of fish .

Until recently, it was not clear how these animals were so transformed. Scientists suspected that evolution had changed the regulation of their development – the so-called fibroblast growth factors.

“They are extremely important for the formation of, say, the teeth that these creatures have lost, for the shape of the snout or the growth of outgrowths – and these are just some examples,” says Susie Bassham, one of the authors from the University of Oregon (USA).

The study of the genomes of both fish showed completely unexpected evolutionary transformations. Some of the genes encoding the mentioned fibroblast growth factors (FGFs) are not present at all.

This also means a restructuring of the gene expression regulation system – biologists have not yet seen anything like this in wild populations.

In addition, the genomes of the “sea dragons” turned out to be rich in repetitive sequences, including the so-called transposons (mobile genetic elements) – sections of DNA that can move around the genome and create their own copies.

Biologists have learned how seahorse relatives got their strange shape 2
Phyllopteryx taeniolatus

For a long time, such sequences were considered ” junk DNA” that does not perform useful functions. However, now “jumping genes” (transposons) and prone to rapid growth of DNA repeats are considered functional and even “hot spots” of rapid evolutionary transformation.

Probably, in many ways, it was they who created such a pretentious masterpiece of evolution as seahorses and their relatives.

Curiously, the authors of the new PNAS article also made high-resolution computed tomography of the “sea dragons”, thanks to which they learned about the structure and development of their leaf-shaped outgrowths. They have nothing to do with the fins of these fish, which are greatly reduced and barely visible.

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