It's a common assumption that auditory information is reserved for living things with ears and that creatures without cochlea—namely plants—don't tune into a bee buzzing or the wind whistling. But a new study suggests the plants are listening, and some flowers even sweeten up their nectar when they sense a pollinator approaching.
Sound is ubiquitous; plenty of species have harnessed the power of sound to their evolutionary advantage in some way or another—a wolf howls and rabbits run; a deer hears a thunder strike in the distance and seeks shelter, and birds sing to attract their mates. Plants have withstood the test of time, so logically so, they must react to such a crucial sensory tool as well, right? This question is the essentially the basis of Tel Aviv University evolutionary theoretician Lilach Hadany's interest in pursuing the new study, reports Michelle Z. Donahue at National Geographic.
Since sound is propagated as a wave, it doesn't always take the complex set of ear bones and hair cells found in mammal ears to detect the presence of sound, just the ability to perceive vibrations.
To test the idea, Hadany and her team looked at the relationship between bees and flowers. The team exposed the beach evening primrose, Oenothera drummondii, to five types of sound: silence, the buzz of a bee from four inches away, and low, intermediate and high pitched sounds produced by a computer, Donahue writes. They then measured the amount of nectar that the flowers produced after being exposed to the sound.
Blossoms exposed to silence as well as high-frequency and intermediate-frequency waves produced the baseline amount of sugar expected in their nectar. However, the blooms exposed to the bee's buzz and low-frequency sounds bumped their sugar content up 12 to 20 percent within three minutes of being exposed to the hum. In other words, when they "heard" a bee approaching, they sweetened their nectar.
Perhaps this isn't too surprising because—although flowers come in all shapes and sizes—so many are actually rather ear-shaped, with petals forming conical or cupped shapes.
To make sure the sound is what was triggering the flowers to produce sugar, and not some other factor, they placed the blossoms in a laser vibrometer, which records very small movements, and replayed the sounds. They found that the bowl-shaped primroses resonated with the bee sounds and the low-frequency sounds, but did not vibrate with the other frequencies. If flower petals were removed, their sense of "hearing" was disabled as well.
"We were quite surprised when we found out that it actually worked," Hadany tells Donahue. "But after repeating it in other situations, in different seasons, and with plants grown both indoors and outdoors, we feel very confident in the result."
The study appears on the preprint service bioRxiv and has not yet been published in a peer-reviewed journal. But Ed Yong at The Atlantic asked several prominent researchers about the quality of the paper and they were impressed by the study. The science of plant communication is rife with pseudoscience and outlandish claims that have never been proven, meaning any claims need to undergo extra scrutiny. Entomologist Richard Karban from the University of California at Davis, who researches interactions between plants and insect pests, tells Yong that the new study is legitimate, and builds on other recent research showing plants can respond to vibrations.
"The results are amazing," he says. "They're the most convincing data on this subject to date. They're important in forcing the scientific community to confront its skepticism."
Hadany calls the science of plant interaction with sound "phytoacoustics" and says there's still a lot left to learn about how plants perceive sound and the mechanism of those relationships.
"We have to take into account that flowers have evolved with pollinators for a very long time," Hadany tells Donahue. "They are living entities, and they, too, need to survive in the world. It's important for them to be able to sense their environment—especially if they cannot go anywhere."
