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Brawn trumps beauty and sex trumps fitness on the evolutionary battlefield

William Muir examines a tank of transgenic Glofish. The fish express a fluorescent protein cloned from sea anemones. (Purdue Agricultural Communication photo/Tom Campbell)

William Muir examines a tank of transgenic Glofish. The fish express a fluorescent protein cloned from sea anemones. (Purdue Agricultural Communication photo/Tom Campbell)

Experiments with zebrafish capture evolution in action as scientists observe the ousting of genetic traits over generations.

In a study released yesterday in the journal Evolution, demonstrated how evolutionary forces led to the extinction of a particular genetic trait in the laboratory.

Researchers from Purdue University studied 18 different groups of zebrafish containing both wild-type males and males that had been genetically modified to produce a fluorescent red glow.

Although female zebrafish were attracted to the splashy glowfish, when it came time to mate, they settled down with the duller, browner, wild-type zebrafish. Well, settled down is an overstatement, they were bullied into mating with the wild guys who chased their pretty competitors away.

Aside from their pushiness with females, the wild-type males and the genetically modified males were both equally fit in standard evolutionary terms: they had the same lifespan and the same level of health and fertility.

What all this means is, genetic adaptations bred into the decorative aquarium fish were not carried on in their offspring because they didn’t have many compared to the wild guys.

“The females didn’t get to choose,” said William Muir, professor of animal sciences at Purdue. “The wild-type males drove away the reds and got all the mates. That’s what drove the transgene [the modified gene] to extinction.”

As a result, the rate at which the “glow gene” appeared in offspring fell rapidly over 15 generations and ultimately disappeared in all but one of the 18 populations the researchers tracked. According to the researchers, this is the first laboratory study demonstrating evolution in action.

“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,” said Richard Howard, Purdue professor emeritus of biology. “This study puts the whole story together.”

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