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June 25, 2001

Method of assessing GMO ecological risk developed at Purdue

WEST LAFAYETTE, Ind. – A model to determine the environmental risks of genetically modified organisms, or GMOs, has been developed by two Purdue University researchers.

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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."

Sources: William Muir, (765) 494-8032; bmuir@purdue.edu

R.D. Howard, (765) 494-8136; rhoward@bilbo.bio.purdue.edu

Writer: Steve Tally, (765) 494-9809; tally@aes.purdue.edu

Purdue Ag Communications: (765) 494-2722; Beth Forbes, Ag News Coordinator, bforbes@aes.purdue.edu; http://persephone.agcom.purdue.edu/AgCom/news/

Purdue News Service: (765) 494-2096; purduenews@purdue.edu


ABSTRACT

Fitness components and ecological risk of transgenic release:

A model using Japanese medaka (Oryzias latipes)

William Muir, Richard Howard, Purdue University

Any release of transgenic organisms into nature is a concern because the ecological relationships between genetically engineered organisms and other organisms (including their wild-type conspecifics) are unknown. To address this concern, we developed a method to evaluate risk in which we input estimates of fitness parameters from a founder population into a recurrence model to predict changes in transgene frequency after a simulated transgenic release. With this method, we grouped various aspects of an organism's life cycle into six net fitness components: Juvenile viability, adult viability, age at sexual maturity, female fecundity, male fertility, and mating advantage. We estimated these components for wild-type and transgenic individuals using the fish, Japanese medaka (Oryzias latipes). We generalized our model's predictions using various combinations of fitness component values in addition to our experimentally derived estimates. Our model predicted that, for a wide range of parameter values, transgress could spread in populations despite high juvenile viability costs if transgenes also have sufficiently high positive effects on other fitness components. Sensitivity analyses indicated that transgene effects on age at sexual maturity should have the greatest impact on transgene frequency, followed by juvenile viability, mating advantage, female fecundity, and male fertility, with the least impact as a result of changes in adult viability.


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