|
 urdue University researchers have found that releasing
a transgenic fish to the wild could damage native populations,
even to the point of extinction. A transgenic organism is one
that contains genes from another species.
 The
Purdue research is part of an effort by Purdue and the US Department
of Agriculture to assess the risks and benefits of biotechnology
and its products, such as genetically modified fish. The study
was published last November in the Proceedings of the National
Academy of Science.
Purdue
animal scientist Bill Muir and biologist Rick Howard used minute
Japanese fish called medaka to examine what would happen if male
medakas genetically modified with growth hormone from Atlantic
salmon were introduced to a population of unmodified fish. The
research was conducted in banks of aquariums in a laboratory
setting.
The
results warn that transgenic fish could present a significant
threat to native wildlife. "Transgenic fish are typically
larger than the native stock, and that can confer an advantage
in attracting mates," Muir says. "If, as in our experiments,
the genetic change also reduces the offspring's ability to survive,
a transgenic animal could bring a wild population to extinction
in 40 generations."
Extinction
results from a phenomenon that Muir and Howard call the "Trojan
gene hypothesis." By basing their mate selection on size
rather than fitness, medaka females choose the larger, genetically
modified but genetically inferior medaka, thus inviting the hidden
risk of extinction.
The transgenic
medaka were produced by inserting a gene construct consisting
of the human growth hormone driven by the salmon growth promoter
into medaka. The viability of groups of modified and conventional
fish were measured at three days of age, and 30 percent fewer
transgenic fish survived to that age. The researchers calculated
that large males had a fourfold mating advantage, based on observations
of wild-type medaka. Computer models then were used to predict
the consequences of the transgenic mating advantage combined
with the reduced viability of the young.
The study
represents scientists policing science, Muir says. "I hope
people understand that scientists are investigating the risks
of biotechnology as well as the benefits, so decisions can be
made with as much information as possible. It's important to
understand the risks so they can be addressed."
Muir also
cautions that the results of his laboratory study should be interpreted
conservatively. "The study does confirm there are significant
risks to natural animal populations associated with the release
of transgenic animals. We assumed a consistent environment with
only one variable -- sexual preference for size coupled with
low life expectancy for the transgenic. The natural world is
not nearly as orderly, and genetic background changes could negate
the Trojan gene," he says.
The dominance
of sexual preference over Charles Darwin's classic theory of
survival of the fittest is not unknown to wildlife specialists
and geneticists. Muir likes to use the example of the male bird
of paradise with its long swells of gloriously colored plumage
as an example: "The male bird of paradise with the longest,
thickest tail attracts the most females. Subsequent offspring
also exhibit the long tail and also compete well for females.
Unfortunately, the birds with the biggest tails also have the
biggest problem escaping predators, who appreciate large birds
pinned in place by their plumage. Obviously, the bird with the
most sex appeal is the also the worst choice as a fit mate. Not
unlike high school, some might say."
The researchers'
next goal is to replicate the study with larger fish of economic
importance in a bigger environment. They're looking for an indoor
swimming pool where they can raise tilapia and check the results
of the medaka study. 
|
aes.purdue.edu. Purdue University News Service, 1132 Engineering Administration Building, West Lafayette, IN 47907-1132; (765) 494-2096