Mustard Evolved To Give Predators An Unpleasantly Spicy Meal
August 31, 2012

Mustard Evolved To Give Predators An Unpleasantly Spicy Meal

Brett Smith for - Your Universe Online

Many plants have developed spicy mechanisms that deter pests from munching on them. Mustard plants, in particular, have evolved their pungent flavor to effectively target and deter specific predators, according to a new study published this week in the journal Science.

Researchers from Duke University, the Max Planck Institute for Chemical Ecology in Germany and the University of Illinois at Urbana—Champaign looked at the variations in two populations of the same species of mustard plant, one from Montana and one from Colorado, in an attempt to see why they produced distinctly different flavors.

"We were able to put this story together all the way from the plants in the dirt to the amino acids in the laboratory," said Tom Mitchell-Olds, a professor of biology at Duke. “That's where the challenge came in."

To facilitate their study, the biologists selected two populations of Boechera stricta because of certain technical advantages and the relative stability of their unique local environments that have been unchanged for the last 3,000 years. This allowed them to discount certain environmental factors.

After using genetic analysis to identify the BCMA gene responsible for producing the different spicy compounds, Mitchell-Olds and colleagues next went into the field to see how both of these plants would survive in each others´ natural habitats.

The researchers planted thousands of mustard plants together in both Colorado and Montana. As expected, each plant population produced their distinctive flavors, regardless of location; however, the difference was the way insect populations responded to each. Montana insects steered clear from Montana plants but demolished the Colorado variety, suggesting that the Montana population specifically targets local pests.

The Colorado pests however consumed both plants equally, puzzling researchers. They theorized that the difference could reveal that the Colorado insect population had a higher tolerance for the spice. Another possibility is that the competition amongst the Colorado bugs is so fierce–it drives them to consume the spicy plants despite the fiery consequences.

In the final stage of the study, the research team engineered Arabidopsis, a relative of the mustard plants, to express the BCMA genes from both the Colorado and Montana populations. The results of this procedure confirmed the genetic mechanism for producing each plant´s unique spiciness. However, when the researchers exposed their creation to different pest population, they found that the spicy compounds deter certain insects and pathogens, but increase vulnerability to others.

Although many questions remain, the international team of biologists has presented a first step in understanding how natural selection has shaped a mustard species' variation over evolutionary time. The results of the study could have a significant agricultural impact as well.

"We've been able to go to places where the environment is intact, where these genotypes have been sitting around for 3,000 years in the place where they evolved in the first place, and do science," Mitchell-Olds said. "This variation we see reflects history. We finally have the tools to find the genes and to understand their influence on physiology and fitness, and that's pretty cool."