The potential of genetic engineering to modify the genetic structure of plants, animals, and microorganisms has only begun to be realized, as have the risks of spread of transgenes to nontarget organisms.The diversity of characteristics that can be engineered is increasing. Combining multiple genetically engineered traits in individual crop varieties is also becoming increasingly common. Efforts are being made to modify insecticidal transgenes, such as the gene for the Bt endotoxin, so they are effective against a wider range of insect types.
Genetic engineering is being extended to many new groups of organisms, and it is already being employed in biological control programs for pests such as the pink bollworm (Pectinophora gossypiella), in which a gene for a fluorescent protein is being introduced to the bollworm as a genetic marker (Thibault et al. 1999). Genetic engineering is spreading to domesticated and semidomesticated animals, forestry and horticultural plants, and aquacultural animals. Genetically engineered fish of several species that grow faster and reach larger sizes in aquaculture have been developed (Muir and Howard 2002). Genes for tolerance by plants and other organisms to insecticides, fungicides, and other pesticides are being sought to permit the increased use of increased dosages of these agents in a manner comparable to the present use of herbicides with herbicide-tolerant crops. Developments such as these would considerably broaden the impacts of pesticide chemicals on all living organisms.
Thus, genetic engineering is setting the stage for future evolutionary change by many organisms. Intensified selection for counter-responses by weeds and animal pests within the crop environment will certainly occur. Because of the potential for transgenes to escape to wild and weedy plants in grasslands, forests, and other environments, however, these evolutionary effects will extend much farther.
How natural ecosystems will be affected by the spread of alien species carrying transgenes is difficult to predict. Questions of what factors make natural ecosystems vulnerable to invasion by alien organisms and what factors enable alien species to invade such ecosystems are themselves of great evolutionary interest. We shall consider these in the next chapter.
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