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West Lafayette, Indiana
June 25, 2001
Sources:
William Muir, (765) 494-8032;
bmuir@purdue.edu
R.D. Howard, (765) 494-8136; rhoward@bilbo.bio.purdue.edu
A model to determine the environmental risks of genetically
modified organisms, or GMOs, has been developed by two Purdue
University researchers.
William Muir, professor of animal science, and Richard Howard,
professor of biology, were funded by the U.S. Department of
Agriculture's Biotechnology Risk Assessment Program to develop a
method to assess the environmental risk posed by genetically
modified fish. They have expanded the model to include all
sexually reproducing organisms, which includes most animals and
plants.
Muir says that such an objective test to assess environmental
risk could actually make biotechnology more readily accepted by
those currently opposed to it, even if the model points out more
problems.
"I think this model could be a
first step to the acceptance of biotechnology," Muir says.
"Without having rules or a way of regulating or measuring risk,
biotechnology will never be accepted. Now we have an objective,
science-based method to measure risk. If a genetically modified
organism shows little or no risk with this set of tests in a
laboratory environment, we're confident that in nature's more
stringent conditions, the organism will be even less of a risk.
These tests are conservative and tend to err on the side of
caution, so we feel the results will be more acceptable to the
public at large."
Using the model, academic scientists, corporations and
government regulatory agencies can now screen genetically
modified plants and animals to determine if their introduction
into the environment could result in an environmental risk.
"What we have here is a model that makes scientific sense, one
that makes common sense," Howard says. "We don't know whether it
makes nature sense, but we can't put transgenically modified
fish into the ocean and watch what happens. So this is the best
we can do."
Although the researchers stress that most genetically modified
products pose little or no ecological risk ‹ and that those that
do will most likely never make it out of the laboratory ‹their
research shows that some genetically modified organisms have the
potential to cause drastic changes in wild populations.
"There are really two types of risk if a transgenic organism
gets loose," Muir says. "One is an invasion risk, where the new
trait spreads through the population and tries to take over,
like the Africanized honey bees. In the process it may either
displace native species or cause some disruptions in the
ecosystem. The other risk is one in which the trait causes the
population to go extinct. We call that the Trojan gene effect."
The model to assess biotech risks was published in the July
issue of the American Naturalist. The paper is available online
at
http://www.journals.uchicago.edu/AN/journal/contents/v158n1.html.
The model looks at factors related to viability and the ability
to reproduce and measures six critical control points, which the
researchers call "net fitness components:"
- Juvenile viability: the
ability of a plant or animal to live long enough to reproduce.
- Age at sexual maturity: the
age at which plants or animals begin to breed.
- Female fecundity: the ability
to produce eggs in animals or seeds in plants.
- Male fertility: the ability of
a male to fertilize eggs or seeds
- Mating advantage: the ability
to attract mates in animals or pollinators in plants.
- Adult viability: the number of
breeding opportunities an animal or plant has during its
lifetime.
"All natural selection passes
through those six control points," Muir says. "If the
modification affects even one of those six factors, then it's
going to have an impact on whether that modified gene increases
or decreases in frequency if released into nature."
By measuring the six factors and inputting the data into the
model, scientists can assess the risk of an introduced gene.
"If the risk factors are conflicting, with some positive,
particularly mating success, and others negative, particularly
adult or juvenile viability, then you're probably going to run
into an extinction risk," Muir says. "If one or more of the
factors is enhanced, while the others remain the same, then
you're going to have an invasion risk. And if one or more are
reduced, while the others remain the same, then there most
likely will be no risk. This is the most desirable situation."
Previous biological theory had stated that because of "survival
of the fittest," if one of the factors were lowered, the plant
or animal would present no threat in the ecosystem. That isn't
always the case in nature, and it certainly isn't the case with
genetically modified organisms, Howard says.
"Biologists often assume that because transgenic organisms have
lower survivorship, they would present no ecological risk,"
Howard says. "But you can't look at one aspect of natural
selection in isolation. When you have interacting aspects of
reproduction and survivorship, you have to consider those
interactions as well, or else you can really be led astray.
"Our results emphasize the need to measure all six factors to
determine risk and use the model to put these risk factors
together into one prediction."
To test their model, the researchers set up an experiment using
a small fish called the medaka, or Japanese rice fish. The fish
were genetically modified with a growth hormone gene, and the
effects of the new gene were measured.
"In medaka we ran into a complicated scenario because we found
that the transgene affected three of the six parameters," Muir
says. "We found that the gene reduced juvenile viability by
about 30 percent, so that was a negative change. But we also
found that it reduced the age at sexual maturity by 14 percent,
and it increased fecundity by 30 percent. So those were both
positive changes for the transgenic fish."
The researchers then constructed a hypothetical introduction of
60 modified fish into a wild population of 60,000 fish. The
model showed that, in this example, the two positive factors
were strong enough to offset the reduced juvenile viability.
"So what we're predicting from the model is that if a growth
hormone was put into this fish, the modified individuals would
increase in the population and you would face an invasion risk,"
Muir says. "Thus, our model shows that ecological risks of
introducing certain genetically modified organisms into the
natural environment are greater than biologists previously
thought."
Muir and Howard are both quick to point out that despite the
risks from biotechnology, they both support biotechnology and
genetically modified foods.
"I think one of the key things in discussing biotechnology is
the potential for good," Howard says. "In terms of genetically
modified fish, the ability to increase production and fish
availability for human consumption is a tremendous benefit. Our
role is to make sure that along with that benefit
doesn't come a really huge environmental cost. We need to reap
all of the benefits of the technology and try to minimize or
avoid the costs."
Muir says that although the test leaves some doubt as to whether
some genetically modified organisms present an ecological risk,
the method does show definitively that others present no risk.
"I think that 80 percent of the things being developed have
little risk, and the other 20 percent there is some question
about," Muir says. "If something falls into that 20 percent, the
company will most likely just stop the development process. The
company will realize that to determine the true risk will take
an enormous amount of resources, so it would be much easier to
develop another product that will pass all of the tests."
Writer: Steve Tally, (765) 494-9809; tally@aes.purdue.edu
Related Web sites:
Howard's professional Web site:
http://www.bio.purdue.edu/Bioweb/People/Faculty/howard.html
Muir's professional Web site:
http://www.ansc.purdue.edu/faculty/muir.htm
--
Jeanne Norberg, Director, Purdue News Service
(765) 494-2084;
jnorberg@purdue.edu
Pager: 423-8662; Home: 449-4986
Fax: (765) 494-0401
http://news.uns.purdue.edu
--
Beth Forbes, Ag News Coordinator
Ag Communications Service
(765) 494-2722
bforbes@aes.purdue.edu
Fax: (765) 496-1117
http://persephone.agcom.purdue.edu/AgCom/news/
Company news release
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