along the hazy On the bottom of the Amazon River, snake-like fish called electric eels hunt in the dark for careless frogs or other small prey. When a human swims by, the fish releases two 600-volt electrical pulses to stun or kill it. This high-voltage hunting strategy is unique, but a few other fish also use electricity: they generate and sense when they navigate muddy, slow-moving waters and communicate with other species through mild electric shocks similar to Morse code weaker voltage.
Often, when several species share an unusual ability like electricity generation, it’s because they are closely related. But electric fish in South American and African rivers span six distinct taxa, in addition to three other marine electric fish lineages. Even Charles Darwin pondered the novelty of their electrical abilities and their strange taxonomy and geographic distribution. exist Origin of Specieswrote, “It is impossible to imagine the steps by which these wondrous organs arose” — not just once, but repeatedly.
A recently published paper scientific progress Help solve this evolutionary mystery. “We’re really just following Darwin, as most biologists do,” said Harold Zakon, an integrative biologist at the University of Texas at Austin and co-senior author of the study. By piecing together genomic clues, his team in Texas and colleagues at Michigan State University revealed how many strikingly similar electrical organs arose in lineages of electric fish isolated over some 120 million years of evolution and 1,600 miles of ocean. It turns out there’s more than one way to evolve an electronic organ, but nature does have some favorite tricks to fall back on.
The electric shocks in the South American and African fish Zakon’s group studied come from specialized electrical organs that extend over most of their bodies. Modified muscle cells called electrocells in the organ create a gradient of sodium ions. When the sodium gate protein in the cell membrane opens, an electric current is generated. “It’s the simplest signal you can imagine,” Zakon said.
In muscles, these electrical signals flow through and between cells to help them contract for movement, but in electrical organs, the voltage is directed outward. The strength of each shock depends on how many electrical cells are firing at the same time. Most electric fish fire just a few at a time, but because electric eels contain an unusually high number of batteries, they can release voltages powerful enough to kill small prey.
In the new work, Zakon, his former research technician Sarah LaPotin (now a PhD student at the University of Utah) and his colleagues reconstructed a key aspect of the evolution of these electronic organs by tracing the fish’s genomic history.
It began 320 million to 400 million years ago when the ancestors of all fish classified as teleosts survived a rare genetic accident that duplicated their entire genome. Whole-genome duplications are often fatal to vertebrates. But because they create redundant copies of everything in the genome, duplications can also open up previously untapped genetic possibilities. “Suddenly, you have the ability to make a whole new pathway, not just a new gene,” said Gavin Conant, a systems biologist at North Carolina State University who was not involved in the study.
Harold Zakon, an integrative biologist at the University of Texas at Austin, is one of the leaders of the new study on the evolution of electric fish. “As most biologists do, we’re really just following Darwin,” he said.Photo: Lynne McAnelly/Quanta Magazine
