Researchers have discovered
that genetically tinkering with fish can cause the opposite effect
of evolution—the survival of the least fit and the eventual
extinction of a species. It would take just one genetically-modified
fish to wipe out local populations of that species if it escaped
into the wild.
William Muir and Richard Howard of Purdue University call GM
genes “Trojan genes,” because "This resembles the Trojan horse,"
says Muir. "It gets into the population looking like something good
and it ends up destroying the population."
Biologists in the U.S. and the U.K. are currently engineering
salmon so that they contain the human growth hormone gene hGH, which
increases their growth rate and size. Muir and Howard don’t think
this is a good idea, so they tested it by putting hGH in embryos of
a Japanese medaka fish, which is a common aquarium fish that is used
in research. They found the GM fish became sexually mature faster
and produced more eggs. Also, the GM males attracted 4 times as many
mates, probably because they were bigger. This means that the hGH
gene will spread quickly through most fish populations.
But here’s the twist: only two-thirds of the GM fish survived to
reproductive age, compared with wild medakas. So the spread of the
growth hormone gene could make populations unable to reproduce and
lead to extinction.
The researchers used a computer model to find out what would
happen if 60 GM fish were placed in a population of 60,000 wild fish
and discovered that the fish population became extinct within 40
generations. A single GM fish could have the same effect, although
it 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. "Sexual selection drives the
gene into the population and the reduced viability drives the
population to extinction."
Professor David Penman, a fish geneticist at the University of
Stirling in the U.K., has discovered that some GM fish modified with
growth hormone have reduced sperm production. "If large males tend
to mate with large females, this would often result in matings
between GM fish," he says. But if the larger GM males have less
sperm, there would be fewer offspring produced, which would
eventually end the species.
The creation of GM corn has wiped out the natural varieties in
Mexico and will probably do the same thing to corn crops in the rest
of the world—but at least we will still have corn. But adding growth
hormones to a fish species can mean there may eventually be no more
of that kind of fish left to eat.
See June 28 news story “What Makes GM Crops Dangerous?”, click here.
Learn the facts about GM foods from “Eating in the Dark” by
Kathleen Hart, click
here and hear her interview on Dreamland radio by clicking
“Listen Now” at the top of our homepage.
For more information, click