What Is the Origin of Skate’s Wings?

Skates, a type of cartilaginous fish, have pectoral fins that resemble wings, allowing them to thrive in benthic ecosystems. However, the molecular basis of this unique trait remains unknown. University College London researcher Ferdinand Marlétaz aimed to investigate the evolutionary origin of these wing-like fins.

Vertebrates evolved alongside key developmental innovations, including different fin structures in cartilaginous fish such as skates and rays. In a 2015 study, scientists at the University of Chicago discovered that repurposed genes allowed skates and rays to evolve their striking, wing-like fins. “The extraordinary anatomy of skate fins comes about by simple tweaks to the processes that make the more normal-looking fins of other fish,” said senior study author Neil Shubin, PhD.

Early in embryonic skate development, the pectoral fins mirrored those of other fish and tetrapods. However, instead of creating one apical ectodermal ridge (AER) per appendage, the genes develop two – one toward the tail and one toward the head. The researchers also found that embryonic skates develop the rear portion of the fin using limb-development genes, while the front portion develops using shoulder genes. The researchers investigated the origin of this phenotypic innovation by studying the little skate (Leucoraja erinacea) as a genomic model using extensive transcriptome resources. They also analyzed a high-quality chromosome-scale genome sequence for the little skate to understand the particular skate morphology.

Batoid fin morphology was significantly affected by functional inhibition of planar cell polarity signaling, confirming that this pathway is a major contributor to batoid fin morphology. Marlétaz says that understanding the morphology and evolution of these animals is important because it can help us understand how novelties emerge in evolution.