New insights on ecological dynamics driven by genetically modified crops

May 06, 2014 Bookmark and Share

Photo credit: Thanasis Anastasiou photostream:

Photo credit: Thanasis Anastasiou photostream:

Genetically modified crops have been integrated as a central component of the agricultural policies of many nations across the globe due to their insecticidal properties.

The type of genetically modified organism (GMO) that Paul Glaum, a Ph.D. student in the Department of Ecology and Evolutionary Biology, researched is a transgenic Bt crop. A transgene is a gene that has been transferred from one organism to another, in this case, a bacterium called bacillus thuringiensis (Bt). When Bt reproduces, it makes an insecticidal protein. “Geneticists have taken the gene for the production of this protein from Bt and put it in maize and many other crops,” said Glaum. “Crops that have been modified to include the genes from Bt produce the protein that kills insects. This is like having a bunch of crops that can now produce their own pesticides.

“While focus on increased yield resulting from the use of Bt crops has overshadowed the concerns of pest populations developing resistance, resistance has been recently discovered in even highly managed fields,” according to Glaum.

“One issue that has received less attention is the resulting set of ecological dynamics from escaped Bt products into wild settings. As an ever increasing number of studies find transgenes outside of their intended usage areas, questions of ecological consequences regarding Bt toxin producing plants and pest species resistant to those toxins in the wild become more pertinent.”

Glaum’s research, “Dual invasion analysis: a general model of novel ecological dynamics due to Bt product and resistant pests in wild settings,” was published in print in the May 2014 issue of Theoretical Ecology, and online in January 2014. Glaum, whose advisor is Professor John Vandermeer, is the sole author.

Glaum used a model to investigate invasion potential of Bt individuals and their Bt-resistant pest populations that have escaped from managed agricultural land into wild or unmanaged settings. Model results show that persistence of the initial invading Bt plant population is possible through an intransitive loop dynamic.

“An intransitive loop is like a game of rock, paper, scissors,” explained Glaum. “Rock beats scissors, scissors beats paper, paper beats rock. So, if we think of this as competition, there is no one winner. If we threw rocks, papers, and scissors into a competitive system, whenever one got too powerful, the one that can beat the powerful option would begin to win. This creates a looping dynamic in ecological systems that can govern population fluctuations.”

This is an approximate analogy for what happens in the Bt system. Bt plants produce the Bt toxin, so they can ‘beat’ the pest. However, the cost of producing the toxin is expensive, so when pests are low, a wild type (nonBt) plant can competively ‘beat’ the Bt plant. This is the energy tradeoff. Finally, the pest can beat the wild nonBt plant by eating it, but cannot eat the Bt plant due to the toxin. There is also an energy cost associated with insects developing resistance to the Bt toxin.

These energy costs create the interplay that allows for nonBt plants, Bt plants, regular pests, and pests resistant to the Bt toxin to coexist in unmanaged settings.

Furthermore, coexistence of wild-type plants and pests, as well as Bt-producing plants and resistant pests, is possible through the dynamics resulting from energy trade-offs.

“Given the growing instances of escaped transgenes discovered in the wild, transgenic Bt should be an area of concern,” Glaum said. “Model results show ecological interactions resultant from energy tradeoffs make Bt transgenes an important crop to monitor for escape from management.”