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201514May11:50

Evo­lu­tion in action: wild-​type zebrafish out­com­pete genet­i­cally mod­i­fied Glofish

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pub­lished 14 May 2015 | mod­i­fied 14 May 2015
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Zebrafish and GlofishPur­due Uni­ver­sity research found that wild-​type zebrafish (Danio rerio) con­sis­tently beat out genet­i­cally mod­i­fied Glofish in com­pe­ti­tion for female mates, an advan­tage that led to the dis­ap­pear­ance of the trans­gene from the fish pop­u­la­tion over time.

The study, the first to demon­strate evo­lu­tion­ary out­comes in the lab­o­ra­tory, showed that mate com­pe­ti­tion trumps mate choice in deter­min­ing nat­ural selec­tion. The find­ings have been pub­lished online on 6 May in the jour­nal Evo­lu­tion.

Mat­ing suc­cess is actu­ally a stronger force of evo­lu­tion than sur­vival of the fittest,” said William Muir, pro­fes­sor of ani­mal sci­ences. “If an organ­ism can’t get a mate, it can’t pass its genes on. In terms of evo­lu­tion, whether it sur­vives or not doesn’t matter.”

Muir and Richard Howard, pro­fes­sor emer­i­tus of biol­ogy, con­ducted a long-​term study of mat­ing suc­cess in mixed pop­u­la­tions of wild-​type zebrafish and Glofish — zebrafish con­tain­ing a trans­gene cloned from a sea anemone that pro­duces a flu­o­res­cent red pro­tein. Although female zebrafish strongly pre­ferred the neon red males to their brown, wild-​type coun­ter­parts, the females were coerced into spawn­ing with the wild-​type males who aggres­sively chased away their trans­genic rivals.

As a result, the rate at which the red trans­genic trait appeared in off­spring fell rapidly over 15 gen­er­a­tions of more than 18,500 fish and ulti­mately dis­ap­peared in all but one of 18 populations.

Dar­win was right: Sur­vival of the fittest works
William Muir, pro­fes­sor of ani­mal sci­ences, Pur­due University »

The females didn’t get to choose,” Muir said. “The wild-​type males drove away the reds and got all the mates. That’s what drove the trans­gene to extinc­tion.” Except for their mat­ing com­pet­i­tive­ness, wild-​type males and Glofish males were sim­i­lar in fit­ness — that is, their health, fer­til­ity and lifes­pan — which was unex­pected since genet­i­cally mod­i­fy­ing an organ­ism often decreases its abil­ity to flour­ish, Muir said. “Nat­ural selec­tion has had bil­lions of years to max­i­mize an organism’s fit­ness for its envi­ron­ment,” he said. “Chang­ing its genet­ics in any way almost always makes an organ­ism less fit for the wild. You’ve ‘detuned’ it.”

The sim­i­lar­ity of the wild-​type zebrafish and Glofish made it pos­si­ble to test mate com­pe­ti­tion and mate choice simul­ta­ne­ously, which few stud­ies have done, Howard said. “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,” he said. “This study puts the whole story together.”

The study also showed the effec­tive­ness of a model Muir devel­oped to assess the poten­tial risk posed to nat­ural pop­u­la­tions by trans­genic organ­isms. The model, which mea­sures six fit­ness com­po­nents, can be used to pre­dict what would hap­pen if a par­tic­u­lar trans­gene were released in the wild. Its premise lies in a sim­ple prin­ci­ple: If a trans­gene makes an organ­ism fit­ter than wild types for an envi­ron­ment, it could pose a risk to nat­ural pop­u­la­tions or the ecosys­tem. If a trans­gene makes the organ­ism less fit, the gene will be weeded out of the pop­u­la­tion over time.

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.”

Based on the model, the researchers pre­dicted that wild-​type males would chase other males and females more than Glofish males would, have greater suc­cess in secur­ing mates and pro­duce more off­spring. The lab­o­ra­tory find­ings con­firmed their predictions.

The study shows that if Glofish were released into the wild, the trans­genic trait would even­tu­ally dis­ap­pear as the result of sex­ual selec­tion. Muir stressed that “the model does not say that even if we find no risks, we should release trans­genic fish into the wild. It sim­ply says what would likely hap­pen if we did.”

The model can be applied to genet­i­cally mod­i­fied plants as well as ani­mals and is one tool used by the U.S. Food and Drug Admin­is­tra­tion to assess poten­tial risks posed by trans­genic organ­isms, he said.

Glofish are the only trans­genic ani­mals approved for sale to the pub­lic by the US Food and Drug Admin­is­tra­tion.



(Source: Pur­due Uni­ver­sity news release, 07.05.2015)


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