That's shocking! Genes reveal electric eels evolved their supercharged muscles separately 200 million years ago
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For the first time, the genome of the electric eel has been sequenced.
This discovery has revealed the secret of how fishes with electric organs have evolved six times in the history of life to produce electricity outside of their bodies.
The research sheds light on the genetic blueprint used to evolve these complex, novel organs.
The genome of the electric eel (pictured) has been sequenced for the first time. The results of a new study indicate that, despite millions of years of evolution, independent lineages of eel developed electric organs in a similar way. Worldwide, there are hundreds of species of electric fish, in six broad lineages
The study was co-led by Michigan State University (MSU), University of Wisconsin-Madison (U-W), University of Texas-Austin and the Systemix Institute.
ELECTRIC EELS AND THEIR SUPERCHARGED MUSCLES
All muscle and nerve cells have electrical potential and a simple contraction of a muscle will release a small amount of voltage.
Between 100 and 200 million years ago, some fish began to amplify that potential.
They evolved electrocytes from muscle cells, which were organised in sequence and capable of generating much higher voltages than those used to make muscles work.
The electric eel is a fish capable of producing electric shocks of up to 600 volts. Despite its name, it is not closely related to true eels.
It has a long, scale-free cylindrical body and a square moth at the end of its snout.
Two organs, known as the Hunter's organ and the Sach's organ, give the fish its ability to generate electric discharges.
When the eel spots prey, it opens the ion channels in these organs, reversing the polarity and creating an electric potential.
This generates an electric current like a battery, which it uses to immobilise small prey.
The shock, however, is not likely to be fatal to humans.
'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,' said Jason Gallant, MSU zoologist and co-lead author of the paper.
'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.'
Worldwide, there are hundreds of species of electric fish, in six broad lineages.
Their diversity is so great that Darwin himself cited electric fishes as critical examples of convergent evolution, where unrelated animals independently evolve similar traits to adapt to a particular environment, or ecological niche.
All muscle and nerve cells have electrical potential and a simple contraction of a muscle will release a small amount of voltage.
But between 100 and 200 million years ago, some fish began to amplify that potential by evolving electrocytes from muscle cells, organised in sequence and capable of generating much higher voltages than those used to make muscles work.
'Evolution has removed the ability of muscle cells to contract and changed the distribution of proteins in the cell membrane; now all electrocytes do is push ions across a membrane to create a massive flow of positive charge,' said Lindsay Traeger, U-W graduate student and co-author of the study.
DNA sequencing is a process through which DNA molecules are 'laid out' and catalogued. It involves a method to determine the order of the bases - adenine, guanine, cytosine and thymine - in a strand of DNA and essentially 'map out' the genome. Pictured is a sequence of DNA
The 'in-series alignment' of the electrocytes and unique polarity of each cell allows for the 'summation of voltages, much like batteries stacked in series in a flashlight,' added Michael Sussman, U-W biochemist.
The additional current required for the power comes from the fact that an eel body contains many millions of such 'batteries' working together and firing their electrical discharge simultaneously.
The new work provides the world's first electric fish genome sequence.
It also identifies the genetic factors and developmental pathways the animals use to grow an organ that, in the case of the electric eel, can deliver a jolt several times more powerful than the current from a standard household electrical outlet.
Other electric fishes use electricity for defense, predation, navigation and communication.
Future MSU research will focus on testing the role of these genes in the development of electric organs, using state-of-the-art transgenic techniques in Gallant's newly constructed laboratory.
The findings were published in Science.
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