Plants Are Capable of Making Complex Decisions

Plants may not be able to think in the same way we do—they lack brains, after all—but new evidence suggests they're capable of making decisions more complex than you'd expect.

Scientists based out of the Helmholtz Center for Environmental Research and the University of Göttingen have discovered that the European Barberry shrub can calculate whether or not to abort its own seeds to prevent parasitic infestations of fruit flies.

The team claims these results are “the first ecological evidence of complex behavior in plants” in their study, published in the March edition of The American Naturalist. “This species has a structural memory and is able to differentiate between inner and outer conditions as well as anticipate future risks,” they concluded.

The researchers were tipped off to the Barberry's defense mechanism when they discovered that its close relative, the Oregon grape shrub, is infested with ten times as many Rhagoletis meigenii fruit flies as the Barberry. Given that the flies lay their eggs in the fruits of both shrubs, the dramatically higher incidence of infestations on the Oregon grape was perplexing.

To get to the bottom of the disparity, 2,000 berries from various regions of Germany were collected, studied for signs of larval infestation, and fed into a Monte Carlo simulation. Lo and behold, it turns out that the Barberry's secret weapon is a knack for calculating probabilities. While many plants have a kneejerk abortive reaction to compromised seeds, the reaction of this particular shrub is much more nuanced.

“If the Barberry aborts a fruit with only one infested seed, then the entire fruit would be lost. Instead it appears to 'speculate' that the larva could die naturally, which is a possibility,” said Hans-Hermann Thulke, one of the study's authors. “Slight chances are better than none at all. This anticipative behavior, whereby anticipated losses and outer conditions are weighed up, very much surprised us. The message of our study is therefore that plant intelligence is entering the realms of ecological possibility.”

Indeed, the plant seems to “understand” that when it has two seeds—one infected and one intact—it's a much better idea to axe both to save the healthy seed, and does so three quarters of the time. But when a fruit only bears one seed, and that ends up infested, the Barberry aborts only five percent of the time, apparently preferring to wait it out and hope for the best.

The Barberry's clever strategy is more than just a botanical insight—it may also end up being the plant's main defense against climate change. Fruit flies have been rapidly expanding their territories as worldwide temperatures warm, and stand to be a consistent menace to their new ecosystems.

The Organization for Economic Co-operation and Development has studied how climate change enables fruit fly invasions, and released a report on the potential havoc they might wreak as they gain traction in new regions.

“Accelerated by global warming […] pest invasions have profound effects on both national and regional economies, on entire ecosystems, on agricultural cropping patterns, on sustainable production of agricultural goods, on pesticide use and on conservation,” [the report](http://www.oecd.org/tad/crp/PapadopoulosSummary report.pdf) [read](http://www.oecd.org/tad/crp/PapadopoulosSummary report.pdf). “Fruit flies comprise a major group of pests including several invasive species […] that threaten the sustainable fruit and vegetables production worldwide.”

The famously adaptable fruit fly has even been shown to rapidly evolve “inversion” mutations during heat waves, that allow it to tolerate higher temperatures. So in learning to ward off these tenacious parasites, the Barberry may have cinched its own evolutionary success. Thinking ahead pays off, even for plants.