If genetically modified organisms are able to survive and reproduce in the environment, some of them will succeed in spreading like 'aliens' throughout natural populations. This process might not be immediately obvious or externally apparent. However, by the time the problem is evident, it may be too late. Genetic engineering can thus endanger the conservation of natural species.
An example: a gene in fruit flies (Drosophila melanogaster) was manipulated using CRISPR/Cas gene scissors to make it similar to one found in monarch butterflies (Danausplexippus). By changing only four base pairs in total, the fruit flies became resistant to toxins produced by certain plants. As a result, the flies can absorb the toxins and become poisonous to their predators. Mass release of such flies could have serious consequences for the food web and ecosystems. Fruit flies, resp. their larvae, are an important source of food for other insects and also amphibians.
Ultimately, although only very small changes in the DNA were needed, a certain combination of changes was necessary to achieve the desired resistance to the toxin. This was due to the fact that this specific gene is involved in several biological processes, i. e. it has so-called pleiotropic effects. It was only after the combination of genetic changes was ‘optimised’ that the flies showed normal vitality and resistance to the toxins in the plants. ‘Monarch Flies’ show, for instance, that it is not solely about the number of genetic changes or their range, but rather a matter of specific patterns of genetic change and the resulting combination of genetic information.
Even if these respective combinations were to actually appear spontaneously in fruit flies, it is by no means certain that these traits would spread through a population. For this to happen, it would be necessary for single individuals to be able to create large, stable populations. Even if the new gene combinations did become established, it would require long periods of time during which ecosystems could adapt. In contrast, flies derived from New GE could be released in large numbers within short periods of time, and thus disrupt the ecosystem.
This example shows: Even minor changes to a single gene can have a significant impact on the natural world, even if no additional genes are inserted into the genome. The gene combination resulting from New GE could, in theory, also emerge from evolutionary processes. However, this would require long periods of time and adaption of ecosystems before larger populations with these gene variants could be established. However, if there were to be large-scale releases of the genetically engineered flies within short periods of time, they could become a threat to biodiversity and the protection of species.