outcome is persistence of both transgenic and nontransgenic genotypes (Hedrick, 2001; Muir and Howard, 2001).
The effect of genetic engineering on fitness can be determined either prospectively or retrospectively. Appendix A of the Scientists’ Working Group on Biosafety (1998) provides a prospective assessment of factors that would affect an organism’s ability to become established in the environment, while Muir and Howard (2001a,b; 2002) provide a retrospective method based on measurement of net fitness components.
From a prospective view, the key factor affecting fitness is transgene functionality within the GE organism. Functionality can be divided into four broad categories: those that increase adaptability of the GE organism to a wider range of environmental conditions, usually through new functionality; those that alter existing traits for improved performance within standard production agriculture; those that produce new or novel products; and those that produce animals or animal products for human medical benefit.
A transgene might increase an organism’s adaptation to a wider range of environmental conditions, for example, by increasing freeze tolerance (Fletcher et al., 1992) or removing a limiting growth factor, perhaps allowing the organism to synthesize an amino acid that was previously limiting, or to digest previously indigestible carbon sources such as cellulose, or to obtain phosphorous from previously inaccessible sources, such as phytic acid (Golovan et al., 2001a,b). Finally, a transgene can be used to increase disease resistance by, for example, disabling retroviruses, producing coat proteins that activate the immune system against certain viruses or that bind to receptor molecules by which viruses enter cells, or by producing antibiotics to protect against bacterial infections (Dunham et al., 2002; Jia et al., 2000; Sarmasik et al., 2002).
Such adaptations also could allow GE animals to invade or persist in ecosystems where they otherwise could not, such as salt or brackish water, while maintaining populations in communities where they normally occur, such as freshwater lakes and streams. Such a combination could result in a sustained invasion of the new community from the species’ original or introduced range until complete colonization results. Hence, a transgene that increases fitness or adaptation increases the probability of establishment and results in the highest level of concern for establishment.