Veits et al. 2019. Flowers respond to pollinator sound within minutes by increasing nectar sugar concentration. Ecology Letters 22: 1483-1492. doi: 10.1111/ele.13331
I’m an ecologist, but it’s only one of the labels I would use to describe myself. Another is ‘obsessive music enthusiast’, and in my professional life I tend to get very excited about any situation where I can find overlap between these two labels. Example: three years ago, I visited the International Congress of Entomology in Orlando, Florida: an enormous, Comic Con-like event where participants could spend five days immersing themselves in the six-legged wonders of the world. Officially, I was there to talk about my work on the functional importance of insect herbivores in grasslands, and to attempt elbow-rubbing with various big names in my field of research. Yet, I found it absolutely necessary to make time for two off-topic talks I’d sniffed out: “Bugs and the blues: Insects as tricksters in early blues music” (Robert K. D. Peterson, Montana State University) and “For the record: The contribution of insects in popular music” (Stephen R. Clarke, USDA – Forest Service).
My search for overlap isn’t confined to instances where nature inspires human musical expression; I get equally excited when I’m presented with examples of nature responding to said expression. Many will have seen the videos of Snowball, the internet’s favorite rhythmically gifted cockatoo, who rose to fame by performing perfectly synchronized dance moves to various pieces of popular music, and whose talents were responsible for the Backstreet Boys’ appearance in the methods section of a Current Biology paper. I love these sorts of stories – love when animals respond to music, however ambiguously (I mean, did Snowball enjoy the beats of “Backstreet’s back”, or was he simply stomping his little foot, demanding a track change? We’ll never know…).
The natural soundscape
While I get excited when nature and music meet, I find nature’s own music equally exciting: singing birds, buzzing insects, wind moving through the trees, the chattering of monkeys up in the canopies (although I confess that chattering monkeys are not commonplace in my everyday natural soundscape of southern Sweden). Some people might not reflect much on the sounds of nature when they are outdoors, but they would likely acutely notice if those sounds disappeared. Sounds are integral to the human experience of nature, and the conservation value of the sounds of nature undoubtedly deserve to be highlighted in conservation efforts. Beyond the human experience, sounds are highly important for communication within and between species, and many animals struggle to hear each other in an ever noisier world, one particularly dramatic example being birds having to adjust their singing time to avoid being drowned out by jet engines.
When you think of the importance of sounds in nature, it’s quite likely that you think about animals. But a recent research example illustrates the importance of sound also for plants, and presents a fascinating and previously undocumented auditory mechanism.
Listening for visitors
The recent article, published in Ecology Letters by Marine Veits and colleagues at Tel-Aviv University, Israel, provides what is likely the first documented example of a plant responding to an airborne sound. In the study, the researchers exposed plants of the beach evening primrose (Oenothera drummondi) to playbacks of different sounds; a recording of a honeybee, recordings of artificial sounds at frequencies similar to and higher than that of the honeybee, and silence. The researchers compared how much nectar the plants produced in response to each sound. When the plant was exposed to the natural sound of honeybee wingbeats, the flowers produced sweeter nectar. The response was quick, occurring within three minutes of playback. It seemed that the flowers were functioning as “ears”, vibrating mechanically in response to the sounds, which triggered the production of sweetened nectar.
Why is this a useful trait for the plant? Well, most importantly it allows for informed resource allocation. If the plant can adjust the sweetness of its nectar based on the presence or absence of pollinators, it doesn’t have to waste important resources on producing sugars when there’s no pollinators around. In other words, it should only have to make an effort to attract pollinators when there are pollinators in the area, receptive to attraction measures.
Plants – good listeners?
The researchers point out that the response of pollinators to plants signaling from a distance has been well studied, but the inverse – how plants respond to pollinators signaling from a distance – hasn’t previously been described. When it comes to plant-animal interactions such as insect pollination, it’s easy to forget that the plant doesn’t just play a passive part in the interaction. Sure, their movements and responses are so much slower than those of their animal collaborators, but move they do, and this study is a beautiful example of how a plant slowly, gently, and oh so quietly responds to its environment.
If this sound-mediated optimization of pollination is disrupted – for example in noisy environments where humans pollute the natural soundscape – it could have consequences for plant populations that might be reliant on sound cues to tell them when it’s time to dial up the sweetness in order to attract a nearby pollinator. This study is a first step towards understanding the role of sound perception in plants, and the authors point out that it triggers interesting follow-up questions. Perhaps plants also respond to the sounds of herbivores, other animals, and even other plants. In any case, this is a detailed, beautiful addition to our knowledge of the multitude of ways through which species interact in nature, and a powerful reminder of the intricacies of what we’re trying to conserve, when we discuss ways to counteract threats against natural ecosystems. And for me, I’ve found myself relating to plants in a new way. Apparently, just like me, they perk up at certain sounds, and they listen for music in their surroundings; in fact, they can even be dependent on that music for surviving.