How Skates and Rays Evolved Their Wings

How did skates and rays evolve their wings? Scientists have taken a closer look at these animals and have found that the development of these fins relied on repurposed genes.

How the limbs of tetrapods, which are four-legged animals, develop is an area of intense research in biology. However, much less is known about how fish acquired their remarkable diversity in fish shape and function.

In order to study how fins evolve and diversity, the researchers analyzed gene expression in the embryos of batoids, which is a group of cartilaginous fish including skates and rays and which evolved from an ancient lineages of shark that dramatically altered its body plan to thrive on ocean or river bottoms. With flat bodies and broad pectoral fins that are fused to their heads, batoids possess one of the most unique appendage shapes among vertebrates.

The researchers found that the pectoral fins of embryonic skates, at least early on, mirrored limb development in other species of fish and tetrapod. A group of genes and growth factors are expressed in precise patterns in the budding appendange, which help create a region that stimulates cell proliferation along the growing edge of the limb and is essential for elongation, organization and proper development.

"What is surprising is that 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 Neil Shubin, lead study author, in a news release.

The findings may reveal a bit more about skates and fish in general.

"Skates appear to have redeployed a preexisting genetic module to the anterior of their fins, which enabled the evolution of their unique shape," said Tetsuya Nakamura, one of the researchers. "A better understanding of these molecular mechanisms will help us answer questions about the general diversity of fish fins-how they changed shapes, what shapes are possible, what molecular kits can be recruited, and ultimately how fins transitioned into tetrapod limbs."

The findings are published in the journal Proceedings of the National Academy of Sciences.

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