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Genetically Modified Organisms as Invasive Species? 307
it warns that, if selection is strong enough, then these indigenous strains will
acquire beneficial traits.
A study of potential gene flow between alien North American gooseberry
species (resistant to the co-evolved American gooseberry mildew) and
mildew-susceptible native British gooseberries provides a very similar picture.
Hybrid seedlings containing resistance genes were found to have a selective
advantage (Warren and James 2006), illustrating the potential for crop
gene escape to alter the ecological behaviour of native British gooseberries in
much the same way as does transgenic disease resistance. Furthermore, plants
containing the alien genes supported significantly more, albeit smaller invertebrates.
The key questions arising from these last two examples are the same as
those we have discussed for transgenic organisms – what impact does the
transgene target (for example, mildew) have on native populations, and what
is the significance of the ‘unpredicted’ side effects of the introduced genes? We
need to understand the mechanisms and impacts of naturally or deliberately
introduced genes to predict the path of invasions. The principles and
processes of gene flow, selection and invasion are essentially the same.
Whether this results in significant changes in biodiversity or ecosystem function
is yet to be documented, and the risk assessment of transgenic organisms
remains to be resolved on a case-by-case basis.
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