Why do sea horses swim upright, look like horses and have male pregnancy?

Researchers said they have sequenced the genome of a sea horse species for the first time and identified the genetic underpinning for certain peculiarities in this equine-looking fish group, which inhabits coastal waters around the world.

Sea horses boast a host of oddities. Males, not females, carry and give birth to babies. They swim upright, not horizontally. They have horselike heads, tubelike snouts and no teeth. They have grasping tails to grip seagrasses and corals.

Their bodies are covered in bony plates. Unlike most fish, they lack tail and pelvic fins. Their eyes work independently, letting them look forward and backward simultaneously. And they can change colors to camouflage themselves.

“They are such iconic animals, one of the examples of the exuberance of evolution,” said evolutionary biologist and genome researcher Axel Meyer of Germany’s University of Konstanz, one of the researchers in the study published in the journal Nature.

“Their numbers are declining due to habitat destruction and harvest by humans,” added molecular biologist Byrappa Venkatesh of Singapore’s Agency for Science, Technology and Research.

The researchers analyzed the genome of the Southeast Asian tiger tail sea horse, which reaches four inches long and boasts a yellow-and-black-banded tail. It had the fastest rate of molecular evolution among any fish whose genome has been studied.

Male sea horses possess a brood pouch. During mating, a female deposits eggs into the male’s pouch. The male fertilizes the eggs internally and carries them in the pouch until they hatch, releasing fully formed offspring into the sea.

A gene that plays a role in egg hatching in other fish underwent duplication in the sea horse and assumed a new role, helping with the evolution of the male pouch.

Genes that in people and other animals play a role in tooth production were mutated in sea horses and lost functionality. Lacking teeth, sea horses use their snout to suck in plankton and other prey.

A gene involved in the development of pelvic fins in other fish and of legs in humans was absent in sea horses. To compensate, sea horses swim by using a small fin on their back that beats rapidly, with steering provided by tiny pectoral fins near the back of the head.

— Reuters

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