William Muir, professor of animal sciences, and Richard Howard, professor of biology, used computer modeling and statistical analyses to examine the hypothetical risks of introducing genetically modified organisms into wild populations.
"We examined these hypothetical situations because the range of new transgenic organisms is almost unlimited," Muir said. "It is constructive for those developing such organisms to be able to anticipate how they could pose a hazard."
The new computer models have shown that the risk of extinction is greater than believed before, identifying three new scenarios in which genetically modified organisms could result in the extinction of a natural population.
"In the broadest sense, this research tells one how to do risk assessment and what GMOs need further containment," Muir said.
In 2000, Muir and Howard found that a release of fish that were larger — and therefore had higher mating success — but also had shorter life expectancy, could drive a wild population extinct in as few as 40 generations. Muir and Howard labeled this the "Trojan gene hypothesis."
But further investigation has found other scenarios that could lead to extinction.
In one scenario, a genetic modification increases the size of the male, which results in the male finding more mates and also living longer. But if the modification also has a third effect of making the male less fertile, the predicted result is that the wild population will be extinct in just 20 generations.
"We consider this an extreme risk," Howard said. "That's the most severe time frame we've encountered so far."
Howard said this risk could arise if fertility was restricted in a genetically modified organism as a way to limit the spread of the gene in the natural population.
"This was the biggest surprise for me, that if you lowered fertility of genetically modified organism the time course to population extinction was faster rather than slower when the genetically modified young have better survival than wild-type individuals," he said. "I still look at the graph of those data and find it amazing."
The researchers also found scenarios in which the introduced gene could spread through the population but not reduce the overall population size. The researchers termed this an invasion risk.
"The invasion risk is an unknown in assessing the overall risk," Howard said. "Given the biology, all we can say is that the gene would increase in the population. We don't know if that would cause a problem or not. In this case you wouldn't really know until you actually released the gene into the population."
The results of the research were published in the most recent issue of the scientific journal Transgene Research. The research was funded by the U.S. Department of Agriculture Biotechnology Risk Assessment Program.
The Purdue research is part of an ongoing effort by Purdue and the USDA to determine the risks of biotechnology, particularly transferring genetic material from one species to another, known as transgenic technology.
"Consumer confidence in the use of transgenic technology will only happen if there is a thorough, unbiased examination of the risks," Muir said.
The most recent study found that some of the most significant risks occurred when the introduced gene increased the viability of the adult organism, such as through improved immune response or resistance to a disease or pathogen.
"It's somewhat counterintuitive that increasing the health of the adult could hurt the overall population, but that is what we found if they had reduced fertility," Howard said.
The scientists say the increased risk from transgenics comes about because such transfers involve one gene from a different species.
"This gene has a mega effect that may confer new functionality on the organism," Howard said.
Traditional breeding, on the other hand, can only affect genes of that species and involves an exchange of many genes, which the scientists call polygenic inheritance.
"Selective breeding is based upon polygenic inheritance where the result is the cumulative effect of many — perhaps hundreds — of genes each with a small effect. In contrast, most genetic modification involves one gene with a major effect," Howard said. "The two methods are not substantially equivalent, although they may be legally regulated as if they are."
Muir and Howard said the genetic background of the modified organism may be a key to potential risk.
A 2001 report by the Royal Canadian Society found that highly domesticated crops, such as corn and soybeans, rarely become weeds in natural settings because "the cultivated species have been genetically crippled through intense artificial selection."
"What this means is that the more wild an animal is, the greater the environmental risk when using that animal to make a transgenic organism," Muir said. "In other words, making a transgenic salmon is going to be more of a risk to the environment than making a transgenic cow."
Muir acknowledges that hypothetical experiments may not reflect what happens in the real world, but he said the experiments err on the side of caution.
"If we show that these plants or animals may be a risk in a laboratory experiment, it could be that they wouldn't be a risk in nature because nature is less hospitable," he said. "It may be that things we find to be a risk in the lab aren't a risk at all in nature. We feel that this is a conservative approach to determining the risk."
To get a more accurate assessment of the risk of a genetically modified organism, a facility would need to be constructed that would replicate the natural environment. Muir said some companies are already considering constructing such testing facilities.
"It's going to cost millions of dollars to build elaborate testing facilities that are as close to a natural setting as possible," he said. "But nobody said this is going to be easy. What's at stake is important enough to spend that kind of money."
Writer: Steve Tally, (765) 494-9809; tally@purdue.edu
Sources:
Richard Howard, (765) 494-8136; rhoward@bilbo.bio.purdue.edu
William Muir, (765) 494-8032; bmuir@purdue.edu
Related Web sites:
Howard's Web page: http://www.bio.purdue.edu/Bioweb/People/Faculty/howard.html
Muir's Web page: http://www.ansc.purdue.edu/faculty/muir.htm
ABSTRACT
Assessment of possible ecological risks and hazards of transgenic fish with implications for other sexually reproducing organisms
William M. Muir and Richard D. Howard, Purdue University
Transgenic technology is developing rapidly; however, consumers and environmentalists remain wary of its safety for use in agriculture. Research is needed to ensure the safe use of transgenic technology and thus increase consumer confidence. This goal is best accomplished by using a thorough, unbiased examination of risks associated with agricultural biotechnology. In this paper we review discussion on risk and extend our approach to predict risk. We also distinguish between the risk and hazard of transgenic organisms in natural environments. We define transgene risk as the probability a transgene will spread into natural conspecific populations and define hazard as the probability of species extinction, displacement, or ecosystem disruption given that the transgene has spread. Our methods primarily address risk relative to two types of hazards: extinction which has a high hazard, and invasion which has an unknown level of hazard, similar to that of an introduced exotic species. Our method of risk assessment is unique in that we concentrate on the six major fitness components of an organism's life cycle to determine if transgenic individuals differ in survival or reproductive capacity from wild type. Our approach then combines estimates of the net fitness parameters into mathematical model to determine the fate of the transgene and the affected wild population.
We also review aspects of fish ecology and behavior that contribute to risk and examine combinations of net fitness parameters which can lead to invasion and extinction hazards. We describe three new ways that a transgene could result in an extinction hazard: 1) when the transgene increases male mating success but reduces daily adult viability, 2) when the transgene increases adult viability but reduces male fertility, and 3) when the transgene increases both male mating success and adult viability but reduces male fertility. The last scenario is predicted to cause rapid extinction, thus it poses an extreme risk. Although we limit our discussion to aquaculture applications, our methods can easily be adapted to other sexually reproducing organisms with suitable adjustments of terminology.
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