Results from a five-year study involving University of Montana plant ecologist John Maron suggest plants can evolve quickly to lose anti-insect defenses when those defensive traits are no longer needed.
Maron collaborated on a study of evening primrose wildflowers in experimental plots growing in New York. The study found that primroses lost defensive traits that protected them from plant-eating moths in only three or four generations when the insects were experimentally suppressed.
“The research demonstrates that evolution can occur quite rapidly in a field setting,” Maron said. “It also shows that in the absence of herbivorous insects the frequency of plants possessing traits associated with herbivore resistance can change rapidly.”
The National Science Foundation funded the research, and results were published in the Oct. 5 issue of Science. Anurag Agrawal of Cornell University was the principal investigator, and he worked with researchers at UM, the University of Toronto and the University of Turku, Finland.
Through natural selection, the wildflowers evolved away from having high concentrations of insect-deterring chemicals and later flowering, which protects against plant-eating larvae that peak early in growing seasons. The primroses also evolved traits making them better able to compete against dandelions, which unexpectedly thrived in the experimental insect-suppression plots.
“When dandelions were liberated from their own herbivores, they became more abundant in the plots,” Maron said. “This altered the competitive environment and selected for primrose genotypes that could handle this increased competition.
“This rapid change in primrose competitive ability was unexpected,” he said. “It shows how interactions influencing one species in an assemblage can in turn affect the evolution of other community members.”