Sea dragons’ genes give clues to their distinctive looks
Even with a lot of fish in the sea, sea dragons stand out from the crowd.
The funky, fabulous fish are adorned with ruffly leaf-like embellishments. Their spines are bent. They are missing their ribs and their teeth. And the responsibility of the pregnancy is taken on by the males.
By sequencing the genomes of two species of sea dragons, University of Oregon (UO) researchers have found genetic clues to the fish’s distinguishing features: They lack an important group of genes found in other vertebrates. Those genes help direct the development of the face, teeth and appendages, as well as parts of the nervous system.
Sea dragons belong to the same family as seahorses and pipefish. “This group is just cool for a number of different reasons,” said Clay Small, a research assistant professor and member of biology professor Bill Cresko’s lab. “But sea dragons are eccentrics in a group of already eccentric fish.”
Small co-led the project with senior research associate Susie Bassham.
“There’s a lot of interest in how malleable things like the head and face are to evolution,” Bassham said.
And sea dragons can be good case studies for those kinds of questions because of the extreme differences they developed quite quickly. The family that includes sea dragons and seahorses branched out about 50 million years ago, which is relatively recent by evolutionary standards.
Bassham, Small and their colleagues report their findings June 22 in the journal Proceedings of the National Academies of Sciences†
In the wild, sea dragons only live off the coast of Australia. That made them difficult to study. But Cresko’s lab gained rare access to tissue samples by working with scientists at the Birch Aquarium in Scripps and the Tennessee Aquarium, who breed sea dragons in captivity.
The researchers sequenced the genomes of two species of sea dragon, the leafy and weedy sea dragon. They compared those genetic sequences to pipefish and seahorses, as well as other less closely related bony fish such as zebrafish and stickleback.
Along with pipefish and seahorses, sea dragons lacked some of the genes that guide development, a possible clue to the origin of their unique shape.
Compared to their closest relatives, sea dragons also contain more than usual amounts of repetitive DNA sequences called transposons. These sequences, also called ‘jump genes’, often copy themselves or move around in the genome. They can cause rapid genetic changes when they insert themselves in the middle of or near a gene, causing the gene to not work as usual.
The team also used a specialized X-ray microscope at UO’s Knight Campus to capture a high-resolution 3D image of a weedy sea dragon. They scanned the foot-long fish in sections and then stitched the images together to form a complete image.
“Nobody had ever depicted a part of a sea dragon in that way, at such high resolution,” Bassham said.
At that level of detail, they were able to see the fine structure of the sea dragon’s bones and also gain insight into how some of the fish’s unique body structures might have evolved.
“We could see that the supporting structures for the leaf-shaped paddles appeared to be elaborations of spines, and then the fleshy appendages were added at the tips,” Bassham said. “It lent evidence to the idea that these (ornaments) are evolutionarily derived from spines.”
The UO scientists hope that making the genome sequences of sea dragons publicly available will be helpful for further research, not only in evolution and developmental genetics, but perhaps in the effort to understand and conserve the rare fish.
San Diego aquarium breeds rare weedy sea dragon in captivity
Clayton M. Small et al, Leafy and weedy seadragon genomes link genetic and repetitive DNA features to the extravagant biology of syngnathid fish, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2119602119
Quote: Sea dragon genes provide clues to their distinctive appearance (2022, June 27) retrieved June 27, 2022 from https://phys.org/news/2022-06-sea-dragons-genes-clues-distinctive.html
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