Nav: Home

How skates and rays got their wings

December 09, 2015

The evolution of the striking, wing-like pectoral fins of skates and rays relied on repurposed genes, according to new research by scientists from the University of Chicago. Studying embryonic skates, they discovered that the rear portion of the fin is built by typical limb-development genes; but the front portion develops through a different set of genes that are usually found in the shoulder areas of other species.

The findings, published in the Proceedings of the National Academy of Sciences on Dec. 7, 2015, shed light on the genetic mechanisms responsible for the evolution and diversification of vertebrate appendages.

"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 senior study author Neil Shubin, PhD, Robert R. Bensley Professor of Organismal Biology and Anatomy at the University of Chicago.

How the limbs of tetrapods, or four-legged animals, develop is an area of intense research in biology, with great strides made in understanding the genetics and molecular mechanisms involved. However, much less is known about how fish acquired their remarkable diversity in fin shape and function -- including at least one set that became adapted for life on land.

To study how fins evolve and diversify, Shubin and his team, led by Tetsuya Nakamura, PhD, postdoctoral fellow at the University of Chicago, analyzed gene expression in the embryos of batoids--a group of cartilaginous fish including skates and rays, which evolved from an ancient lineage of shark that dramatically altered its body plan to adapt to life 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 discovered 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 appendage, which help create the apical ectodermal ridge (AER) -- a region that stimulates cell proliferation along the growing edge of the limb and is essential for elongation, organization and proper development.

Most species have one AER per appendage, but the team found that skates will develop two -- one that directs pectoral fin growth toward the tail, while the other directs growth toward the head.

Remarkably, different groups of genes appear to control the two regions. Among the many genes involved, the 5'Hox family of transcription factors and the Fgf10 growth factor play a central role in forming and maintaining the AER in most fish and tetrapods. In skates, these genes were present and functioning as normal in the fin region growing toward the tail. The region oriented toward the head, however, was maintained by a separate group of genes -- most prominently, 3'Hox transcription factors and Fgf7.

"Even though the posterior and anterior regions of a skate fin look similar, gene expression is totally different," Nakamura said. "This indicates that they have very different mechanisms that control growth of the anterior portion, which are not found in tetrapods or other fish. I think these genes are very important for the evolution of skate or stingray shapes."

Although the 3'Hox and 5'Hox gene families and Fgf7 and Fgf10 respectively are related to each other, they normally perform different functions at different locations. In most species, 3'Hox genes and Fgf7 are observed at the base of the budding limb, around where the shoulder would eventually be. The expression of these genes in the pectoral fin, and their role in creating a second AER, appears to be a unique adaptation possessed by batoids.

The researchers are now further exploring the genetic mechanisms involved in the development of batoid fins, as well as other distinctive fin shapes in other species.

"Skates appear to have redeployed a preexisting genetic module to the anterior of their fins, which enabled the evolution of their unique shape," Nakamura said. "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."
-end-
The study, 'Molecular mechanisms underlying the exceptional adaptations of batoid fins,' was supported by The Brinson Foundation, the Japanese Society for the Promotion of Science, Uehara Memorial Foundation, Brazilian National Council for Scientific and Technological Development, and the National Institutes of Health. Additional authors include Jeff Klomp, Joyce Pieretti, Igor Schneider and Andrew R. Gehrke.

University of Chicago Medical Center

Related Evolution Articles:

Chemical evolution -- One-pot wonder
Before life, there was RNA: Scientists at Ludwig-Maximilians-Universitaet (LMU) in Munich show how the four different letters of this genetic alphabet could be created from simple precursor molecules on early Earth -- under the same environmental conditions.
Catching evolution in the act
Researchers have produced some of the first evidence that shows that artificial selection and natural selection act on the same genes, a hypothesis predicted by Charles Darwin in 1859.
Guppies teach us why evolution happens
New study on guppies shows that animals evolve in response the the environment they create in the absence of predators, rather than in response to the risk of being eaten.
Undercover evolution
Our individuality is encrypted in our DNA, but it is deeper than expected.
Evolution designed by parasites
In 'Invisible Designers: Brain Evolution Through the Lens of Parasite Manipulation,' published in the September 2019 issue of The Quarterly Review of Biology, Marco Del Giudice explores an overlooked aspect of the relationship between parasites and their hosts by systematically discussing the ways in which parasitic behavior manipulation may encourage the evolution of mechanisms in the host's nervous and endocrine systems.
More Evolution News and Evolution Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Erasing The Stigma
Many of us either cope with mental illness or know someone who does. But we still have a hard time talking about it. This hour, TED speakers explore ways to push past — and even erase — the stigma. Guests include musician and comedian Jordan Raskopoulos, neuroscientist and psychiatrist Thomas Insel, psychiatrist Dixon Chibanda, anxiety and depression researcher Olivia Remes, and entrepreneur Sangu Delle.
Now Playing: Science for the People

#537 Science Journalism, Hold the Hype
Everyone's seen a piece of science getting over-exaggerated in the media. Most people would be quick to blame journalists and big media for getting in wrong. In many cases, you'd be right. But there's other sources of hype in science journalism. and one of them can be found in the humble, and little-known press release. We're talking with Chris Chambers about doing science about science journalism, and where the hype creeps in. Related links: The association between exaggeration in health related science news and academic press releases: retrospective observational study Claims of causality in health news: a randomised trial This...