Sighting a sharp sea dragon, floating among the algae, embellished with leaf-like ornaments moving in the ocean currents, is truly a spectacle to behold.
But sea dragons have more things than the diver looks like. As dazzling as they are, sea dragons also lack teeth, have no ribs and their spines are curved and bent.
Now, scientists have found genetic clues that could explain why sea dragons look so surprisingly distinctive: not only are their genomes full of repetitive fragments of DNA that drive evolution, but they also lack a group of genes. which give rise to teeth, nerves, & c. and facial features in other animals.
Genome exploration of the sea dragon genomes has “raised a veil over the evolution of specific features of the sea dragon” and “has revealed intriguing evolutionary facets of this family of unusual vertebrates, the Syngnathidae as a whole.” write the team behind the studio on a new piece of paper.
Sea dragons belong to the same family as pipe fish and seahorses, the Syngnathidae, which are known to have evolved into male pregnancy.
“This group is great for several different reasons,” says evolutionary genomics researcher Clayton Small of the University of Oregon, who led the study along with fellow researcher Susan Bassham.
“But sea dragons are weird in a group of fish that are already weird.”
To find out why, Small, Bassham and the team sequenced the genomes of two species of sea dragons: the leafy sea dragon and the common sea dragon or weeds, both found in fresh water off the coasts more southern Australia.
Drifting along with their leaf-like fronds that help camouflage them in the rocky reefs covered in algae, these slender fish can be hard to spot.
So elusive, in fact, that the third (of only three) species of sea dragon, the rare ruby sea dragon (which was not sequenced in this study) was only first sighted in the wild in 2017.
The three species of sea dragons are revered for their fantastic, colorful body shapes and long tubular snouts that suck crustaceans, but the ruby sea dragon seems to have lost the leafy appendages that the others show, and evolution removes the ruffles. extravagant.
Scientists believe that sea dragons evolved their extravagant features quite rapidly, over the last 50 million or so years, as they and seahorses branched out to form a new family.
What’s less clear is how they came to look so distinctive, though. Thus, for this study, researchers at the University of Oregon teamed up with scientists from the Birch Aquarium of the Scripps Institution of Oceanography and the Tennessee Aquarium, to analyze what samples they had of sea dragons bred in captivity.
It turns out that sea dragons, compared to their closest relatives, pipe fish and seahorses, have in their genetic code a surprisingly large number of repetitive DNA sequences called transposons, also known as “genes”. jumpers “.
Transposons are so mobile, they jump through the genome, that they can create rapid genetic changes, which could explain why sea dragons evolved so quickly.
Compared to two distant relatives, zebrafish and hawthorns, the genomes of leafy sea weeds and weeds do not have a piece of genes that play an indispensable role in other vertebrates, which contain instructions on how to form facial structures, teeth, limbs and even parts of the central nervous system.
Although researchers were tempted to speculate that the loss of these genes could explain how sea dragons developed elongated facial features and fabulous flying, more research will be needed to investigate the evolutionary history of sea dragons and their parents.
But researchers hadn’t finished yet, and they also imagined a one-foot-long male male weevil sea dragon specimen with high-resolution X-ray microscope scans, which revealed that the ornamental appendages probably evolved into from the thorns.
“We saw that the supporting structures of the blade blades looked like thorn elaborations [with fleshy appendages] added to the extremes, ”Bassham says.
The team also noticed that these bony supports differed from the hardened, ossified bones found in the fins of most bony fish and instead appeared to be rigid by a core of collagenous tissue, adding to the story of how the unique body structures of the sea dragon arose. to be.
As much as sea dragons have evolved, the results are glorious, even glamorous. As far as we know, sea dragons may still have some more secrets hidden in their genome, which can be discovered with more genetic comparisons.
The study was published in PNAS.