Scientific Asia: New research indicates that some species of sea robins, which are peculiar ocean fish that live on the bottom, use taste buds on their legs to locate and identify prey on the seafloor.
Sea robins are such skilled hunters that other fish follow them. They hope to find some fresh prey. This is according to the authors of two new studies published Thursday in Current Biology. Sea robins use their six leg-like appendages to walk along the ocean floor.
The fish were unintentionally found by the coauthor of both publications, David Kingsley, during a summer 2016 discussion at the Marine Biological Laboratory in Woods Hole, Massachusetts. Kingsley is the Rudy J. and Daphne Donohue Munzer Professor in the Department of Developmental Biology at the Stanford University School of Medicine.
Before leaving to catch a flight, Kingsley stopped by a tiny public aquarium where he saw sea robins and their delicate fins—feather-attached bird wings—as well as leglike appendages. The sea robins on display, according to Kingsley’s email, “completely spun my head around because they had the body of a fish, the wings of a bird, and multiple legs like a crab.”
Curious about this, Kingsley and his team decided to study sea robins in the lab. Their research uncovered many surprising facts. It found genetic differences between sea robin species. It also traced the origins of their unique traits. Their leg-like fins, for example, evolved to be sensory organs.
The research team’s latest results show that evolution creates complex adaptations in specific environments. For example, sea robins can “taste” prey with their incredibly sensitive, quick-moving limbs.
An extremely uncommon creature
Sea robins’ characteristic extremities are extensions of their pectoral fins, according to Amy Herbert, a postdoctoral researcher at Stanford’s Kingsley Lab and coauthor of the study.
“We chose the term ‘legs’ due to the remarkable ability of these appendages to walk,” Herbert wrote in an email. But neither their structure nor their position resembles that of human “legs.”
While some fish species have modified pectoral or pelvic fins to enable walking or perching, sea robins are better at walking and digging because each leg can move independently, according to Herbert.
Lead study author Corey Allard made a comment stating, “Sea robins are an example of a species with a very unusual, very novel trait.” “We intended to ask, ‘How do you make a new organ?’ using them as a model.” Allard is a postdoc in the lab of study coauthor and Harvard professor Nick Bellono, in the department of molecular and cellular biology at Harvard.
Returning to Bellono’s lab, the researchers studied a few sea robins to determine if they could unearth buried prey. The fish were seen by the scientists swimming and walking in short bursts.
In addition, they were observed picking at the sand-covered tank bottoms, showing no signs of where potential prey might be hidden.
“We were shocked to learn that they were incredibly skilled at it and could even find single amino acids and ground-up, filtered mussel extract,” Bellono stated.
The study authors transported more sea robins to the lab to investigate. Upon arrival, they found that the birds were a different species with different traits.
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Genetically distinct walking fish
In addition, they were observed picking at the sand-covered tank bottoms, showing no signs of where potential prey might be hidden.
“We were shocked to learn that they were incredibly skilled at it and could even find single amino acids and ground-up, filtered mussel extract,” Bellono stated.
The study authors transported more sea robins to the lab to carry out their investigation, but when they arrived, they found that the birds belonged to a completely different species and had different characteristics.
Like human tongue’s taste buds, the digging sea robins’ shovel-shaped legs were covered in projections called papillae. The legs of the non-digging sea robins were fashioned like rods and lacked papillae.
The fact that species that dig are limited to certain areas, like the sandy shallow waters of New England and the upper eastern Atlantic seaboard, suggests that the fish have only recently evolved this trait, the scientists concluded after comparing the evolutionary histories of the fish’s legs and doing genetic variation studies on the fish.
“We believe that there is a 10–20 million-year gap between digging and non-digging species, so papillae would have needed to emerge after that,” Allard stated.
Although every species of sea robin possesses appendages resembling legs, only a few possess the large sensory organs necessary for tasting their surroundings, according to Kingsley.
According to the study authors, digging sea robins relies on a gene called tbx3a. It builds their papillae, which causes them to dig. It also helps develop their unique fin adaptations. The authors of the study also found that Tbx3 is involved in the development of limbs in humans, mice, chickens, and other fish species.
“It’s quite wild, but this fish used the same genes that help build our limbs to grow legs, and it used those same genes to find prey by using its tongue to taste food,” Bellono said.
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So, why did only a few sea robins develop this special sensory ability? Scientists have come up with two main theories to explain it
One is that, according to Herbert, “using the legs to uncover buried prey” gives them a new method of finding food. Another is that in some settings, sea robins may find it more energy-efficient to walk than to swim.
Jason Ramsay, an assistant professor of biology at Rhode Island College, explains that sea robins are special among walking fish. Their pectoral fins, known as walking fin rays, are highly flexible and feature unique skeletal and muscular adaptations that enable them to walk on the seafloor.
Ramsay, in an email, stated, “A common question is, did these walking rays evolve due to selective pressures for a walking or sensory function, or both?” “More evidence from these new studies suggests that it was most likely the latter-most scenario.”
Ramsay, in an email, stated, “A common question is, did these walking rays evolve due to selective pressures that support a walking or sensory function, or both?” “More evidence from these new studies suggests that it was most likely the latter-most scenario.”
Herbert is opening a lab at the University of Chicago, while Allard is launching his own at Harvard. The specific mechanisms underlying the evolution of the sensory appendages of sea robins are something that both researchers are eager to learn more about.
This news originally published on CNN.
