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Genetically modified fish outcompeted in evolution experiment

"Darwin was right: Survival of the fittest works," study author William Muir said.

By Brooks Hays
Genetically modified fish outcompeted in evolution experiment
Purdue University Professor William Muir examines a tank of fish, both wild zebra fish and genetically modified Glofish. Photo by William Muir/Purdue University

WEST LAFAYETTE, Ind., May 7 (UPI) -- A unique long-term study at the University of Purdue offered biologists the chance to study evolution in real time -- a first. Over several years, researchers observed 18 populations of zebra fish (some wild, some genetically modified), as they reproduced 15 generations.

The traits of the modified zebra fish were less and less apparent in the successive generations, suggesting competition among mates (not mate preference) is the main driver of natural selection.

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The modified fish were dubbed Glofish for their fluorescent appearance. To create the Glofish, scientists spliced a transgene cloned from a sea anemone into the zebra fish's genome. The modification caused the fish to produce a fluorescent red protein, just like the anemone. The visible marker made it easy to track the genetic influence of the Glofish over time.

Researchers found that across 15 generations (and more than 18,500 fish), the red glow vanished completely, despite the fact that (in isolation) female zebra fish preferred the modified Glofish to their wild counterparts. The wild fish simply outcompeted their altered peers for the affection of the females.

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"The females didn't get to choose," William Muir, a professor of animal sciences at Purdue, explained in a press release. "The wild-type males drove away the reds and got all the mates. That's what drove the transgene to extinction."

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Usually genetic modifications lead to a less physiologically sound fish. But the Glofish generally matched the zebra fish in their health, fertility and lifespan. Still, they were outcompeted.

"I've lectured on evolution for 25 years and never found a study that linked the mechanisms of evolution with the pattern of evolutionary outcomes," Muir said of the work of he and his research partner, biology professor Richard Howard. "This study puts the whole story together."

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It also confirms that as long as genetic modifications don't improve the fitness of a species, the genetic influence of modified specimens released into the wild will eventually fade away.

"Darwin was right: Survival of the fittest works," Muir said. "If we make a transgenic organism that has reduced fitness in the wild, evolution takes over and removes it. Nature experiments with mutations all the time, and it only saves the best of the best."

The new research was published in the journal Evolution.

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