One GM Fish Let Loose Can Wipe Out Wild Populations
12/1/99
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Title: One GM fish loose in the wild can wipe out wild populations
Source: New Scientist
http://www.newscientist.com
Status: Copyright 1999, contact source for permission to reprint
Date: December 1, 1999
Byline: Matt Walker
A SINGLE genetically modified fish could turn Darwinian evolution
upside down and wipe out local populations of the species if released
into the wild, biologists warn. They add that other organisms could
face the same risk from transgenic relatives.
William Muir and Richard Howard of Purdue University in West
Lafayette, Indiana, made the discovery while modelling ecological
risks associated with genetically modified organisms (GMOs). They
have dubbed their idea the "Trojan gene" hypothesis. "This resembles
the Trojan horse," says Muir. "It gets into the population looking
like something good and it ends up destroying
the population."
The researchers studied fish carrying the human growth hormone gene
hGH, which increases growth rate and final size. Biologists in the US
and Britain are experimenting with salmon engineered in a similar
way, although no one has yet begun commercial production.
Muir and Howard included hGH in embryos of a fish called the Japanese
medaka (Oryzias latipes), a common aquarium fish that is widely used
in research. They found that modified individuals became sexually
mature faster than normal fish and produced more eggs.
Other experiments using non-modified fish also showed that larger
males attracted four times as many mates as their smaller rivals.
This effect is also known in salmon. Muir predicts that bigger,
engineered fish would enjoy the same advantages. So the hGH gene
would quickly spread through a fish population.
But Muir and Howard also found that only two-thirds of engineered
medaka survived to reproductive age compared with wild medakas. So
the spread of the growth hormone gene could make populations
dwindle and eventually become extinct.
To quantify this, the researchers plugged their results into a
computer model to find out what would happen if 60 transgenic
individuals joined a wild population of 60 000 fish. The population
became extinct within just 40 generations. Even a single transgenic
animal could have the same effect, they found, although extinction
would take longer.
"You have the very strange situation where the least fit individual
in the population is getting all the matings-this is the reverse of
Darwin's model," says Muir. "The sexual selection drives the gene
into the population and the reduced viability drives the population
to extinction." The researchers say their results are the first
evidence that GMOs could have catastrophic consequences on their
own species.
David Penman, a fish geneticist at the University of Stirling,
welcomes the discovery. But he says there is evidence that some
transgenic fish modified with growth hormone have reduced sperm
production and mating success. "If large males tend to mate with
large females, this would often result in matings between
transgenics," he adds. This would decrease rather than increase the
spread of the gene.
But John Beringer of Bristol University, a former chairman of the
British committee that advises the government on GMOs, says the
research is a warning. "It would make it very difficult for anyone
at the moment to approve the release of GM fish carrying growth
hormone," he says. "I would have to give a great deal of
consideration about whether that's an intelligent route to go down."
Muir says that the model may prove an invaluable tool in assessing
the dangers of GMOs. He hopes to test its predictions in tightly
controlled fish farm ponds.
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Author: Matt Walker From issue New Scientist dated 4th December 1999
Source: Proceedings of the National Academy of Sciences (vol 96, p 13
853)
References:
1. http://www.eurekalert.org/cgi/users/toc
2. mailto:claire.bowles@rbi.co.uk
3. http://www.newscientist.co.uk/
4. mailto:newscidc@idt.net
5. http://www.newscientist.com/
6. http://www.eurekalert.org/cgi/users/toc