Potential for and consequences of naturalized Bt products: Qualitative dynamics from indirect intransitivities
Advances in genetic modification technology and the production of human-altered genomes have led to an array of genetically modified organisms utilized to address numerous global issues. The human need-based development of these modified organisms often presents unprecedented phenotypes which will interact with the world’s existing biodiversity in unknown ways. One such example is Bt transgene crops proliferating because of their application to food security issues due to their resistance to pest insects. While threats to long term viability of Bt crop use due to resistance evolution in pests have been extensively investigated, issues regarding the effects of Bt transgene crops on existing ecosystems and the biodiversity contained therein have seen less scrutiny. In particular, the long-term dynamics in the case of a naturalized Bt product has not received the attention it deserves. Here we note that the ecosystem structure emerging from a naturalized Bt crop is, qualitatively, an intransitive loop. Based on this insight, we develop a theoretical community model to investigate how this intransitive structure affects the invasion potential of the Bt phenotype into unmanaged settings and how it alters existing plant-pest community dynamics in the process.
Model results indicate that the intransitive nature of the system has the potential to facilitate long term persistence of naturalized Bt transgenes by shifting community dynamics. This shift in community dynamics is dependent on the inherent natural characteristics of each of the populations in question as well as the relative abundance and timing of the Bt escape/invasion event. Post-invasion dynamics are particularly dependent on the ability of Bt transgenes to compete with wild-type plants when pest densities are low. Such dynamical variety in potential outcomes across parameter and phase space makes predicting the outcome of naturalized Bt products particularly difficult in the field.