Mysterious fish living on the ocean floor has legs to walk

The research, published in two papers in Current Biology, could have far-reaching implications for understanding trait development across species, including humans.

In Short

• Sea robin's 'legs' are actually modified pectoral fins
• The team discovered two distinct species of sea robins
• The research is published in two papers in Current Biology

In a new study, researchers have uncovered new insights into evolutionary adaptations by examining the unusual "walking" abilities of sea robins, bottom-dwelling fish that use leg-like appendages to navigate the ocean floor.

The research, published in two papers in Current Biology, could have far-reaching implications for understanding trait development across species, including humans.

Corey Allard, a postdoctoral fellow at Harvard University, stumbled upon these peculiar fish during a visit to Cape Cod's Marine Biological Laboratory in 2019.

Intrigued by their unique characteristics, Allard and his colleagues set out to investigate how sea robins use their legs and what genetic factors control their development.

The study revealed that sea robin "legs" are actually modified pectoral fins, with three on each side of the body. Through careful observation and experimentation, the researchers confirmed that these appendages function as bona fide sensory organs, capable of detecting both mechanical and chemical stimuli.

In a serendipitous twist, the team discovered two distinct species of sea robins with different leg structures and capabilities.

Prionotus carolinus possesses shovel-shaped legs covered in papillae, similar to taste buds, allowing them to dig for buried prey. In contrast, P. evolans has rod-shaped legs without papillae, used primarily for locomotion and probing.

This distinction led researchers to conclude that the papillae represent an evolutionary sub-specialisation, potentially a relatively recent adaptation. The finding offers a unique opportunity to study how organisms develop novel traits in response to specific environmental pressures.

The genetic component of the research, led by Amy Herbert and David Kingsley at Stanford University, employed advanced techniques such as transcriptomics and genomic editing to identify the gene transcription factors responsible for leg formation in sea robins.

By creating hybrids between the two species, they were able to explore the genetic basis for the differences in leg shape and function.

The implications of this research extend beyond marine biology. The genetic transcription factors controlling sea robin leg development are also found in the limbs of other animals, including humans.

This connection could provide valuable insights into the evolution of bipedalism in our own species, which occurred approximately 6 million years ago.