Electric Fish Genomes Reveal How Evolution Repeats Itself | Quanta Magazine

The electric eel is one of several species of freshwater fish in South America that generate electricity to navigate, communicate, hunt or defend themselves. Fish in Africa independently evolved electric organs that are strikingly similar, though the molecular details of their operation are different.

Even Charles Darwin mused on both the novelty of their electrical abilities and the strange taxonomic and geographic distribution of them in On the Origin of Species, writing, “It is impossible to conceive by what steps these wondrous organs have been produced” — not just once, but repeatedly.

The South American and African fish that Zakon’s group studies get their zap from specialized electric organs extending along much of their body. Modified muscle cells called electrocytes in the organs create sodium ion gradients. When sodium-gate proteins in the membranes of the electrocytes open, this produces a burst of current. “It’s about the simplest signal you could imagine,” said Zakon.

It began between 320 million and 400 million years ago, when the ancestor of all fish classified as teleosts survived a rare genetic accident that duplicated its entire genome. Whole-genome duplications are often deadly for 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 capacity to make a whole new pathway, instead of just one new gene,” said Gavin Conant, a systems biologist at North Carolina State University who was not involved in the study.

the various lineages of fish independently hit on the strategy of modifying their muscle tissue to create electrical organs, and they even did so by making their sodium pumps work selectively in different tissues. But they diverged in precisely how they regulated the pumps.

But for Zakon, it’s the convergent solutions that are most helpful in addressing a fundamental puzzle of biology: If you could rewind the course of evolution, would it play back the same way? Seeing a unique innovation is “fascinating,” he said, but “it doesn’t answer the question, ‘Was there only one way to get there?’” The mix of convergence and divergence seen in organ systems like those of the diverse electric fish offers a much richer view of how predictable — and quirky — biology can be.