Sea robins are fascinating creatures, exhibiting characteristics of fish, birds, and crabs. Recent research reveals that the legs of the sea robin serve more than just walking; they function as actual sensory organs to seek out hidden prey while digging. This research is presented in two studies that appeared in the Cell Press journal Current Biology on September 26.
“This fish has developed legs using the same genetic mechanisms that shape our limbs, and it has adapted these legs to sense prey using the same genes our tongues use for tasting food—it’s quite remarkable,” explains Nicholas Bellono from Harvard University in Cambridge, MA.
Together with David Kingsley from Stanford University and their colleagues, Bellono initially did not set out to examine sea robins. Their interest arose during a visit to the Marine Biological Laboratory in Woods Hole, MA. After observing other fish trailing behind the sea robins—likely impressed by their ability to locate buried food—the researchers decided to investigate further. They took some sea robins back to their lab and confirmed that these fish could indeed detect and unearth powdered mussel extract and even individual amino acids.
According to one of the new studies, sea robins possess legs adorned with sensory papillae, each with dense connections to touch-sensitive neurons. These papillae contain taste receptors and exhibit chemical sensitivity that prompts the sea robins to dig.
“We were initially captivated by the legs that are characteristic of all sea robins and distinguish them from most other fish,” says Kingsley. “We were taken aback by the significant variation in sensory structures present on the legs of different sea robin species. This reveals multiple layers of evolutionary innovation, from the differences between sea robins and other fish to the diversity among sea robin species, as well as variations in both structure and behavior.”
Further developmental research indicated that these papillae are a crucial evolutionary advancement that enables sea robins to thrive on the ocean floor in ways that other creatures cannot. The second study delved deeper into the genetics behind the fish’s distinctive legs. The researchers employed genome sequencing, transcriptional profiling, and hybrid species studies to uncover the molecular and developmental mechanisms involved in leg formation.
Their investigations revealed an ancient and preserved transcription factor known as tbx3a, which plays a significant role in the sensory leg development of sea robins. Genome editing efforts demonstrated that this regulatory gene is essential for the normal development of their legs. The same gene is also vital for the formation of the sensory papillae on the sea robins’ legs and their digging behaviors.
“Although many characteristics may appear novel, they are typically constructed from genes and modules that have been around for a long time,” Kingsley remarked. “That’s the essence of evolution: modifying existing components to create something new.”
The research indicates that we can now deepen our understanding of complex traits and their evolutionary processes in wild organisms, not just in established model organisms. The researchers are eager to explore the specific genetic and genomic alterations that prompted the evolution of sea robins.
