June 27, 2014
The Shocking Story Of How Some Fish Evolved Electric Organs
redOrbit Staff & Wire Reports - Your Universe Online
By sequencing the genome of the electric eel for the first time, researchers have discovered how certain types of aquatic creatures were able to develop organs that allow them to produce electricity outside of their bodies.
Publishing a paper in the latest edition of the journal Science, scientists from Michigan State University, University of Wisconsin-Madison, University of Texas-Austin and the Systemix Institute explain how they identified the molecules that evolved and converted a simple muscle into a unique anatomical feature unique to these specific types of creatures.
According to the researchers, the muscle independently evolved a total of six times in a wide range of environments, including the watery forests of the Amazon region to deep water marine environments. Through their efforts, the authors have determined the genetic and developmental pathways responsible for these complex, novel organs.
“It’s truly exciting to find that complex structures like the electric organ, which evolved completely independently in six groups of fish, seem to share the same genetic toolkit,” Michigan State zoologist and co-lead author Jason Gallant said in a statement Thursday. “Biologists are starting to learn, using genomics, that evolution makes similar structures from the same starting materials, even if the organisms aren’t even that closely related.”
UW-Madison biochemistry professor Michael Sussman, who first started investigating the myogenic electric organ approximately a decade ago, added that his team’s efforts provide evidence to support the notion of a half-dozen electric fish lineages. Each of them evolved independently, using essentially the same genes and cellular pathways to create an electric organ, then using the new organs for communication, defense, hunting and navigation.
The authors reported that they examined the genomic basis of the convergent anatomical and physiological origins of these organs by assembling the genome of the Electrophorus electricus, and then sequencing electric organ and skeletal muscle transcriptomes (sets of all RNA molecules produced) from three unique lineages.
“Our results indicate that, despite millions of years of evolution and large differences in the morphology of electric organ cells, independent lineages have leveraged similar transcription factors and developmental and cellular pathways in the evolution of electric organs,” the study authors wrote.
Their research was funded by the National Science Foundation (NSF), the WM Keck Foundation and the National Institutes of Health (NIH).
While there are six broad lineages of electric fish, UW-Madison explained that there are hundreds of different types of creatures in those groups. In fact, their taxonomic diversity was reportedly so great that Charles Darwin used electric fish to illustrate the concept of convergent evolution, or evolution in which unrelated animals independently evolve similar traits in order to adapt to a specific environment or ecological niche.
The newly published paper features the first draft assembly of the complete genome of an electric fish, the South American electric eel. This electric organ of this particular eel is capable, in some cases, of delivering a charge several times more powerful than a standard household electrical outlet’s current.
“In addition to sequencing and assembling DNA from the electric eel genome, the team produced protein sequences from the cells of the electric organs and skeletal muscles of three other electric fish lineages using RNA sequencing and analysis,” the Wisconsin university added. By conducting a “computationally intense comparative study” using all that information, the researchers were able to reach their conclusions about the evolution of the organ.