Cambridge: Sea robins, fascinating creatures with the body of a fish, bird-like wings, and crab-like walking legs, have long puzzled researchers. Now, a new study, published in Current Biology on September 22, 2024, reveals that these unusual “legs” are more than just a means of locomotion, they are highly specialized sensory organs used to detect buried prey.
Nicholas Bellono, a researcher from Harvard University, who co-led the study reveals that, “Sea Robins is a fish that grew legs using the same genes that contribute to the development of our limbs and then repurposed these legs to find prey using the same genes our tongues use to taste food pretty wild.”
Sea Robins: Not an ordinary fish
Bellono, alongside David Kingsley of Stanford University, stumbled upon the sea robins during a trip to the Marine Biological Laboratory in Woods Hole, MA. Observing other fish following sea robins, seemingly drawn to their prey uncovering abilities, the team became interested in this unique behavior. They decided to investigate further, bringing several sea robins back to their lab to study.
The findings were exciting. The sea robins were found to be able to detect mussel extract and even single amino acids buried in the substrate, uncovering them with the help of their walking legs. These legs, unlike most fish fins, are covered in sensory papillae that house dense nerve endings and taste receptors. This allows the sea robins to sense chemicals and touch, driving them to dig for hidden prey.
Evolutionary innovation
Kingsley discovered that, “We were originally struck by the legs that are shared by all sea robins and make them different from most other fish.”
The two studies delved deep into the evolutionary and genetic factors behind this adaptation. The team found that the sea robins’ sensory papillae represent a key evolutionary innovation, allowing these fish to thrive in their seafloor environment. Genome sequencing and transcriptional profiling revealed that an ancient and conserved transcription factor plays a crucial role in the development of both the sea robins’ legs and their sensory structures.
Genome editing experiments confirmed that this gene is essential for the proper formation of the sea robins’ sensory papillae and their digging behavior.
Understanding evolution in new ways
Kingsley explained that, “Although many traits look new, they are usually built from genes and modules that have existed for a long time.”
The discovery highlights the complexity of evolutionary innovation and demonstrates how organisms adapt by repurposing existing genetic components. The researchers are now eager to explore the genetic changes that led to the unique evolution of sea robins.
This research opens the door to studying complex evolutionary traits in wild organisms, expanding our understanding beyond traditional model species.