Herbicidal interference: Glyphosate drives both the ecology and evolution of plant-herbivore interactions

The coevolution of plants and their insect herbivores reflects eco-evolutionary dynamics at work—ecological interactions influence adaptive traits, which feed back to shape the broader ecological community. However, novel anthropogenic stressors like herbicide, which are strong selective agents, can disrupt these dynamics. Little is known about how the evolution of herbicide resistance may impact plant-herbivore interactions.

We performed a common garden field experiment using Ipomoea purpurea (common morning glory) and the herbicide glyphosate (Roundup) to investigate the ecological effects of herbicide exposure on insect herbivory patterns and assess the potential evolutionary consequences.

We find that plants treated with glyphosate experienced higher levels of herbivory and altered chewing herbivory damage patterns. Additionally, we found that glyphosate resistance is positively associated with herbivory resistance, and uncovered positive selection for increased glyphosate resistance, suggesting that selection for increased glyphosate resistance has the potential to lead to increased herbivory resistance.

Positive selection for glyphosate resistance, coupled with the detection of genetic variation for this trait, suggests there is potential for glyphosate resistance—and herbivory resistance via hitchhiking—to further evolve. Our results show that herbicides can not just influence, but potentially drive the eco-evolutionary dynamics of plant-herbivore interactions.

Methods
Plant growth, resistance level to glyphosate and herbivory, and seed number produced were measured from Ipomoea purpurea during a common garden field experiment. Data has been processed and cleaned to reflect the contents of this study. Scripts for the analyses in this study are also included.