Sea robins are peculiar bottom-dwelling fish. They have six crablike legs, fins that resemble wings, and the body of a fish. Specifically, the legs are of interest, as they contain taste buds that the fish uses to walk and simultaneously sense the presence of prey. In fact, they are so skilled at digging up prey from the seafloor using their legs that other fish follow the trails of sea robins to snag any uncovered prey. Two new studies published in the journal Current Biology brought light to this behavior.
One of the co-authors of the studies, David Kingsley, came across the fish in 2016 at the Marine Biological Laboratory in Massachusetts. According to him, his head spun at the sight of the fish, and he could not recall any other organism with such a diverse set of organs ranging from wing-like fins to crablike appendages.
Kingsley followed up his interest by studying sea robins in lab settings, unveiling genetic secrets responsible for the unusual traits and differences between species of sea robins. The research also shows how evolution can lead to excellent traits such as sensitive appendages— sea robin’s legs can taste.
According to Amy Herbert, a postdoctoral scholar at Kingley’s lab, the special appendages are not true legs; instead, they are modified pectoral fins. Lead author Corey Allard said that they want to use sea robins as a model to understand how new organs are formed.
The researchers tested whether sea robins could root out buried prey. They found that the fish alternated between swimming and walking, occasionally scratching the sand bed under which prey was buried. Surprisingly, they were found to be very adept at uncovering food from beneath the sand surface.
The researchers brought more sea robins into the lab to continue their research. Although these fish looked similar, in reality, they were of a different species that didn’t dig up buried food. The digging sea robins (Prionotus carolinus) had protrusions that acted like taste buds, while the non-diggers (Prionotus evolans) had rod-shaped appendages lacking papillae.
On the genetic side of the study, the scientists revealed that a regulatory gene called tbx3a is responsible for the development of the papillae. The Tbx3 gene also plays a vital role in limb formation in humans, mice, and chickens. Sea robins have used this gene to develop limb-like appendages and repurpose them to taste food.
The next step for the ongoing research about the sensory limbs of sea robins will take a turn toward the evolutionary pathways, both of which will be studied by Allard and Herbert.
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