Electric Fish Genomes Reveal How Evolution Repeats Itself

Along the u At the bottom of the Amazon River, zigzag fish known as electric eels scour the dark in search of careless frogs or other small prey. When a fish swims past, the fish releases two 600-volt electrical pulses to stun or kill it. This high voltage hunting tactic is unique, but some other fish also use electricity: They generate and sense weaker voltages when moving through muddy waters, in slow motion, and when communicating with their fellows through mild shocks resembling morse code.

Usually, when several species share an unusual ability like generating electricity, it is because they are closely related. But electric fish in rivers in South America and Africa span six distinct taxonomic groups, and there are three other lines of marine fish in addition to them. Even Charles Darwin pondered both the novelty of their electrical abilities and their strange taxonomic and geographical distribution in Above Origin of the species, write“It was impossible to conceive according to the steps in which these miraculous organs were produced” – not once but many times.

One recent paper published year Scientific advance help unravel this evolutionary mystery. “We really just watched Darwin, as most biologists do,” says Harold Zakon, an integrative biologist at the University of Texas, Austin and a senior co-author of the study. By piecing together genomic clues, his team in Texas and colleagues at Michigan State University discovered how some of the same electrical organs appear in electric fish lines about 120 million apart. years of evolution and 1,600 ocean miles. As it turns out, there are many ways to develop electric organ, but nature still has some favorite tricks.

The South American and African fish Zakon’s team studied are made of specialized electrical organs that extend along most of their bodies. Modified muscle cells called galvanic cells in organs produce sodium ion gradients. When the sodium gate proteins in the galvanic cell membrane open up, this generates an electric current. “It’s the simplest signal you can imagine,” says Zakon.

In muscles, these electrical signals flow through and between cells to help them contract to perform movements, but in electrical organs, the voltage is directed outward. The strength of each shock depends on the number of galvanic cells firing at the same time. Most electric fish shoot only a few at a time, but because electric eels have an unusually high number of galvanic cells, they can discharge voltages powerful enough to kill small prey.

In the new work, Zakon, former research technician Sarah LaPotin (now a doctoral candidate at the University of Utah) and his other colleagues reconstructed this important aspect of the evolution of these electrical organs by tracing the genomic history of fish species.

It began 320 million to 400 million years ago, when the ancestors of all fish classified as teleosts survived a rare genetic accident that copied its entire genome. Whole-genome copies are often fatal to vertebrates. But because they make redundant copies of everything in the genome, copies can also open up previously untapped genetic possibilities. “Suddenly you have the ability to create a whole new pathway, instead of just a new gene,” says Gavin Conanta systems biologist at North Carolina State University who was not involved in the study.

Harold Zakon, an integrative biologist at the University of Texas, Austin, is one of the leaders in new research into the evolution of electric fish. “We’re really just watching Darwin, as most biologists do,” he said.Photo: Lynne McAnelly / Quanta Magazine

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