But they diverged in precisely how they regulated the pumps. So in a textbook case of convergent evolution, 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. It was temporarily inactive in young fish but turned back on when an entirely different set of genes took over control of the sodium channel in the electric organ as the fish matured. In one oddball lineage of South American fish, the gene did still function in muscle. In most of the South American fish, the pump was just missing from the muscles-the sodium-pump gene was largely inactive because it was missing an essential control element that specifically boosts the expression of the sodium pump in muscle.
In the muscle tissue of the African fish, the sodium-pump gene was still functional, but like a lock with no key, it could not activate without helper molecules that muscle tissue did not make. And when Zakon and his colleagues looked at how the electric fish turned off the gene, they were surprised to discover that different lineages of electric fish did it differently. As it turns out, there’s more than one way to evolve an electric organ, but nature does have some favorite tricks to fall back on.īut crucially, before any electric organ-specific adaptations could be adopted, that second copy of the gene first had to be deactivated in muscle cells-otherwise, the emerging electrocyte capabilities would have interfered with movement. By piecing together genomic clues, his team in Texas and colleagues at Michigan State University uncovered how a number of strikingly similar electric organs arose in electric fish lineages separated by roughly 120 million years of evolution and 1,600 miles of ocean. “We’re really just following up on Darwin, as most biologists do,” said Harold Zakon, an integrative biologist at the University of Texas, Austin and co-senior author of the study. 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.Ī recent paper published in Science Advances helps to unravel this evolutionary mystery. But the electric fish in the rivers of South America and Africa span six distinct taxonomic groups, and there are three other marine lineages of electric fish beyond them. Normally, when several species share an ability as unusual as generating electricity, it’s because they’re closely related. Original story reprinted with permission from Quanta Magazine, an editorially independent publication of the Simons Foundation whose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences.
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