The white-striped goby uses its legs to search for food on the seafloor
Annick Grierson
A striking fish that lives on the Atlantic Ocean’s ocean floor has evolved legs, but they’re not just for walking: The appendages are new tongue-like sensory organs that it uses to find prey buried on the seafloor.
Great-billed Skylark (Prionotus carolinus) have three legs on each side of their body that extend from the base of their pectoral fins. The legs are derived from structures within the pectoral fins called fin rays.
During a research trip to Woods Hole, Massachusetts, Nicholas Verono of Harvard University and his colleagues heard stories about the hunting prowess of common murres and decided to bring some live specimens back to the lab.
The team wanted to see if the fish lived up to its reputation for being good at finding prey: “To our surprise, it was very good at finding prey, even discovering capsules filled with crushed and filtered mussel extract and a single amino acid,” says Verono.
The researchers then collected more fish and discovered that the second group was good at walking, but had trouble finding prey buried in the sand.
“This time, the new murres couldn’t find anything, even though they happily feed on prey at the surface,” Verono says. “We thought maybe we were doing something wrong, but it turns out we’d caught a different species by chance.”
The team discovered by chance a banded murre (Prionotus evolans They walk, but are specialized in hunting unburied prey.
“When we compared digging and non-digging animals, the feet were clearly different, and the sensory papillae in the digging feet were clearly visible,” Bellono says.
These papillae are projections that contain taste receptors and touch neurons, and are similar to the papillae that make up the taste buds on the human tongue.
Many other fishes have evolved modified pectoral and pelvic fins that enable them to walk and perch, says team member Amy Herbert of Stanford University in California. “But what’s unique about this blue auk is that, whereas other fishes typically use their entire pectoral or pelvic fins for this purpose, this one can move its legs independently and quite quickly, making it particularly adept at both walking and digging,” Herbert says.
The team also investigated the genes that drove the evolution of murres’ unique legs, finding that their development is controlled by an ancient regulatory gene called “murre.” Translator.
“It’s normally expressed in specific localized regions of fin and limb buds in all kinds of animals, from fish to mammals,” says team member David Kingsley, also from Stanford, “This is a great example of how we can refine an ancient, shared tool to create a new body part.”
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