A SCUBA expedition in Australia and New Zealand to find the rare embryos of an unusual shark cousin enabled American and British researchers to confirm new developmental similarities between fish and mammals.
Elephant fish, a relative of sharks, utilize the same genetic process for forming skeletal gill covers that lizards and mammals use to form fingers and toes, researchers at the University of Chicago and the University of Cambridge found. The precise timing of when and where that gene is expressed during embryonic development produces dramatic anatomical differences between elephant fish and their close relatives, the dogfish.
The study, published online January 10th by the Proceedings of the National Academy of Sciences, confirms that organisms separated by hundreds of millions of years of evolution share similar genetic programs for body formation.
"The research highlights how evolution is extremely efficient, taking advantage of preexisting mechanisms, rather than inventing new ones," said Andrew Gillis, PhD, at the University of Cambridge and lead author. "By simply tinkering with the timing of when or where a gene is expressed in an embryo, you can get very different anatomical outcomes in adults."
"You have a common nail that's used for many different pieces of furniture," said Neil Shubin, PhD, Robert R. Bensley Professor of Organismal Biology & Anatomy at the University of Chicago and senior author of the paper. "This esoteric fish with this esoteric anatomical system is showing us something very fundamental about the evolutionary tree: that there's a common process at work among disparate types of organisms."
The holocephalans are a family of fish that share a cartilage-based skeleton with better known animals such as sharks and rays. Another shared feature is the presence of appendages called branchial rays, structures that grow outward from the skeleton's central gill arches. While sharks form
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University of Chicago Medical Center