Somewhere between four and six percent of all flowering plants use some form of deception to lure in pollinators. For instance, they can appear to be a source of food or even a potential mate. The pollinators, being unable to detect the illusion, are drawn in and rewarded with little more than a dusting of pollen. Research into the deceptive nature of these plants and how they evolved is ongoing.
One of these studies, recently published in Frontiers in Ecology and Evolution, sheds light on the deception strategy used by the plant Aristolochia microstoma. Uniquely, this flower lures pollinating insects by emitting the stench of dead invertebrates.
Insects head toward the smell of other dead insects
Credit: T. Rupp, B. Oelschlägel, K. Rabitsch et al.
A. microstoma is a purple-brown flower found in Greece. It typically blooms close to the ground, as seen in the above image. This is unusual, as most Aristolochia species have bold and easily seen flowers well above the ground. Additionally, this flower tends to be horizontally oriented, as opposed to the more vertical structure of similar species' flowers. A. microstoma is known to smell like decay, often to the displeasure of humans walking near it.
Pollinators stumble into the flower and — not unlike Hotel California — find themselves unable to leave. Their movements pollinate the plant. Later, they are covered in pollen from the male part of the flower before being released. The cycle then repeats as the insects fall for the same tricks again.
Enter the coffin fly
To learn more about the flower's strange traits and how that relates to its pollination, the authors collected 1457 flowers from three sites in Greece, two on the Peloponnese and one west of Athens. Of the samples, 72 percent were in the first, female stage of blooming. (These flowers go through two stages, first female, then male.) These samples contained 248 arthropods, but only a collection of Megaselia scalaris — also known as coffin flies — were found carrying pollen, suggesting that it is a typical pollinator of the flower.
How fitting, given the smell.
Before this study, it was presumed that A. microstoma was pollinated by ground dwelling pollinators, such as ants. It isn't too surprising that flies would be a primary pollinator, though. After bees, flies are the second most important pollinator on the planet. Many plants have scents and appearances that seem to be trying to attract flies. Unsurprisingly, few of them are known for smelling pleasant.
Fool me once, fool me twice
Between the smell and the location, it is possible the flower simulates a food source or breeding area for the flies well enough to fool them repeatedly.
Additionally, the researchers used gas chromatography to analyze the chemicals and compounds that give the flowers their unique scent. Sixteen compounds were found, including sulfur- and nitrogen-containing molecules, both likely contributors to the powerful odor of the plant.
These compounds included the alkylpyrazine 2,5-dimethylpyrazine. This compound has a unique aroma — decaying beetles, mouse urine, and roasted nuts — so it is unlikely to be used as a perfume. It also can be found in cigarettes and is occasionally used as a food additive for flavor purposes.
Few plants produce this compound, leading the authors to conclude that the plant is producing it to attract specific pollinators. They also mention that the decaying remains of vertebrate animals don't produce this compound either, further strengthening the idea that the plant is trying to smell like decaying insects.
Study co-author Stefan Dötterl from the Botanical Gardens at the Paris-Lodron University of Salzburg explained, "Our results suggest that this is the first known case of a flower that tricks pollinators by smelling like dead and rotting insects rather than vertebrate carrion."
The authors note that the next area of study is to see how fond potential pollinators are of this particular odor. Studies hoping to answer that question are already underway. Let us hope the bugs like it, as it seems nobody else does.
There's a short story by Roald Dahl called The Sound Machine. It involves a man who invents a machine that allows him to tune into the frequency of surrounding plant life. When he first tries it, he can hear the shrieking of the roses, as his neighbor trims and cuts them. Then, he hears the soft, low moan of a tree being cut with an axe. Traumatized, he destroys his machine and goes to help the wounded tree.
This might not be as far-fetched as we think. Trees have a vibrant and complicated life. And while it's a stretch to say that they can "scream," it's not too far off — they really do emit high-frequency distress sounds.
Sociable trees
Olympic National ParkCredit: Alex Berezow
In his wonderful book, The Hidden Life of Trees, Peter Wohlleben explains just how amazing trees (and relatable!) these organisms are. For instance, trees are highly sociable. They have short, hair-like tips at their roots that combine with tiny fungi, allowing them to communicate with other trees — not unlike a phone line. These root tips act like a kind of "awareness" for trees, and they use them to detect if a neighboring tree is of the same species or if it's a sapling. Trees are constantly checking what's going on around them.
It gets better. Trees support and nurture one another. If a nearby tree (of the same species) is sick, or dying even, other trees will feed it sugar and nutrients. Similarly, a parental tree will nurture its sapling for centuries before finally giving way for its offspring to grow into the same light they've enjoyed for hundreds of years. There have even been cases of "relationships" among trees, where their roots become so enmeshed that they share all their nutrients. Poignantly, if one partner tree dies, or is cut away by human hands, the other's death is not far behind.
What's more surprising is that trees have been shown not only to have "memories" of a sort but can also pass these on to their young. Certain trees, for instance, will bloom only after "counting" a particular number of suitably warm days. If they had no sense of memory, they would have to start the count afresh every day. What's more, if a tree has suffered from a particularly harsh drought, they will adapt their water consumption habits. These habits are then, somehow, passed onto saplings through the soil.
Urban trees are socially isolated
SeattleCredit: Alex Berezow
Most of Wohlleben's work is about forests, especially primeval, untouched ones. But, for most of us, our everyday interaction with trees comes from the ones dotted along a sidewalk or those that line a park. What do urban conditions do to trees?
First, the trees we see in our cities and towns are often distantly spaced and consist of a variety of species. This leads to attractive and colorful scenes, but it means that all the benefits of sociability are removed. Trees are denied a support network. They have no parents to nurture them, teach them, and bring them to a slow and gradual maturity.
Second, streetlights interfere with trees' natural cycles. It might sound odd, but trees actually have a form of "sleep" during the nighttime in which their branches sag slightly and water density in the trunk and roots increases. Artificial light confuses this.
What a tree wants
From a tree's perspective, the biggest problem is that humans can't help but see them in terms of what they do for us. They're lumber to chop, shade to rest under, structures to climb, or vistas to enjoy. None of these are bad things. But, just like a human, a tree in isolation can't thrive. It can't flourish as it ought to on its own terms.
We are all invariably bound to experience the world through human eyes and from within a human lifetime. We want a tree to grow quickly and to bloom on demand. But trees live on an entirely different timescale. In ancient forests, trees can live for centuries quite easily, and the oldest trees we know of go back millennia.
One is reminded of the Ents in J.R.R. Tolkein's Lord of the Rings, who are sentient tree creatures. They talk, move, and think far slower than the Hobbits they meet and are surprised by how hasty and pushy they are. One says, "My name is growing all the time, and I've lived a very long long time; so my name is like a story." The problem is that we see the story of a tree only in terms of a human life.
Trees are remarkable things, and they live, grow, and behave in quite incredible ways. And, as is always the case, the more we learn about a thing, the more we can come to respect it.
Jonny Thomson teaches philosophy in Oxford. He runs a popular Instagram account called Mini Philosophy (@philosophyminis). His first book is Mini Philosophy: A Small Book of Big Ideas.
- Venus flytrap leaves shut in response to physical touch, salt water, or thermal stimuli.
- A team of scientists from Berlin have captured the magnetic charge that accompanies the closing of the plant's trap.
- Incredibly sensitive, non-invasive atomic magnetometers picked up the elusive signal.
For many children, the revelation that there's such a thing as a Venus Flytrap, Dionaea muscipula, is an amazing moment. The choppers of the sneaky plant predators are like something out of a fairy tale gone wrong. Adults can't help but be fascinated by them too, and now scientists at Johannes Gutenberg University Mainz (JSU) and the Helmholtz Institute Mainz in Germany have discovered something new that's surprising about these little demons: Every time they entrap prey, they give off a measurable magnetic charge.
"We have been able to demonstrate that action potentials in a multicellular plant system produce measurable magnetic fields, something that had never been confirmed before," says lead author Anne Fabricant.
Guilt as magnetically charged
The plants' bivalved snap trap (left), side view of a destained trap lobe (right)
Credit: Fabricant, et al./Scientific Reports
According to Fabricant, the finding isn't that much of a shock: "Wherever there is electrical activity, there should also be magnetic activity," she tells Live Science. And it is electrical activity in the form of action potentials that trigger its maw—really a pair of leaf lobes—to close when a hapless bug lands inside them, attracted by the nectar with which the plants bait their trap.
Along the inner surfaces of the lobes are trichomes, hair-like projections that cause the trap to close when they're disturbed by prey. One touch of a trichome is unlikely to cause the trap to shut — perhaps a mechanism that helps the plant avoid wasting energy on false alarms. A couple of touches, though, and it's chow time. The lobes come together as the bristles at their edges intertwine to help contain the prey. As the traps compress the trapped insect, its own secretions such as uric acid cause the trap to shut even more tightly, and then digestion begins.
In any event, just because the JSU researchers had reason to suspect the plant would give off a magnetic charge, catching it doing so was not a simple task.
Reading the Venus flytrap's magnetic output
Average action potential and corresponding magnetic signals
Credit: Fabricant, et al./Scientific Reports
"The problem," says Fabricant, "is that the magnetic signals in plants are very weak, which explains why it was extremely difficult to measure them with the help of older technologies." Still, where there's a will: "You could say the investigation is a little like performing an MRI scan in humans."
It's not just trichome flicks that trigger the trap — it will also close if triggered by salt-water, or with an application of either hot or cold thermal energy. The researchers applied heat via a purpose-built Peltier device that wouldn't introduce any background magnetic noise to mask or overwhelm the faint magnetic signal they were seeking. For the same reason, the experiments were conducted in a magnetically shielded room at Physikalisch-Technische Bundesanstalt (PTB) in Berlin.
The researchers used atomic magnetometers to measure the planets magnetic charges. The atomic magnetometer is a glass cell containing a vapor of rubidium atoms. When the traps were triggered, the magnetic charges released changed the spins of the atoms' electrons.
The researchers picked up magnetic signals at an amplitude of up to 0.5 picoteslas. "The signal magnitude recorded is similar to what is observed during surface measurements of nerve impulses in animals," says Fabricant. It's over a million times weaker than the Earth's own magnetic field.
Biomagnetism
Other researchers have detected magnetic charges coming the firing of animal nerves — including within our own brain. The phenomenon is referred to as "biomagnetism." Since other plants have action potentials, they may also generate biomagnetism, though less research has been done on them.
It's to other plants that the attention of the JSU team now turns, as they go looking for even smaller magnetic charges from other species. In addition to providing new understanding of nature's use of electricity, non-invasive detection technologies such as the one employed by the group could one day be utilized for more insightful monitoring of crops as they respond to thermal, pest, and chemical influences.
There are a growing number of examples of animals' evolutionary path diverting around humans and human encroachment. From the increase of tuskless elephants to changing fox snouts, this biological trend, though worrying, is well-documented. Now researchers in China have discovered a wildly growing plant that has adapted by developing camouflage that makes it less likely to get picked by human hands. Nobody likes us.
The study was conducted by botanist Yang Niu of the Kunming Institute of Botany in China, in collaboration with sensory ecologist Martin Stevens of the University of Exeter in England. "It's remarkable to see how humans can have such a direct and dramatic impact on the coloration of wild organisms, not just on their survival but on their evolution itself," Stevens tells University of Exeter News.
The research is published in Current Biology.
Fritillaria dealvayi
The plant is Fritillaria dealvayi, and its bulbs are harvested by Chinese herbalists, who grind it into a powder that treats coughs. The cough powder sells for the equivalent of $480 per kilogram, with a kilogram requiring the grinding up of about 3,500 bulbs. The plant is found in the loose rock fields lining the slopes of the Himalayan and Hengduan mountains in southwestern China.
As a perennial that produces just a single flower each year after its fifth season, it seems Fritillaria used to be easier to find. In some places its presence is betrayed by bright green leaves that stand out against the rocks among which which it grows. In other places, however, its leaves and stems are gray and blend in with the rocks. What's fascinating is that the bright green leaves are visible in areas in which Fritillaria is relatively undisturbed by humans while the gray leaves are (just barely) visible in heavily harvested areas. Same plant, two different appearances.
2/2: The picture on the left shows a Fritillaria delavayi in populations with high harvest pressure, and the one on… https://t.co/oriBNZGcsV— University of Exeter News (@University of Exeter News)1605891854.0
How we know we're the cause
There are other camouflaging plants, but the manner in which Fritillaria has developed this trait strongly suggests that it's a defensive response to being picked. "Many plants seem to use camouflage to hide from herbivores that may eat them — but here we see camouflage evolving in response to human collectors."
"Like other camouflaged plants we have studied," Niu says, " we thought the evolution of camouflage of this fritillary had been driven by herbivores, but we didn't find such animals." His close examination of Fritillaria leaves revealed no bite marks or other signs of non-human predation. "Then we realized humans could be the reason."
In any event, says Professor Hang Sun the Kunming Institute, "Commercial harvesting is a much stronger selection pressure than many pressures in nature."
Credit: maron/Adobe Stock
The study
Since herbalists have been plucking Fritillaria from the rocks for 2,000 years, one might hope a record would exist that could allow researchers to identify areas in which the plant has been most thoroughly picked. There is no such documentation, but Liu and Stevens were able to acquire this type of information for five years (2014–2019), tracking the harvests at seven Fritillaria study sites. This allowed them to identify those areas in which the plant was most heavily harvested. These also turned out to be the locations with the gray-leaf variant of Fritillaria.
Further supporting the scientists' conclusion that gray Fritillaria was more likely to evade human hands and live long enough to reproduce was that participants in virtual plant-identification tests confirmed the species was hard to spot in the wild.
"It's possible that humans have driven evolution of defensive strategies in other plant species, but surprisingly little research has examined this," Stevens notes.
Hang Sun says such studies make clear that humans have become drivers of evolution on our planet: "The current biodiversity status on the earth is shaped by both nature and by ourselves."
- Canadian biotech company Medicago is growing a vaccine candidate in Nicotiana benthamiana.
- An Australian relative to tobacco, plant-based vaccines could be cheaper and more reliable than current methods.
- Medicago just completed phase 3 clinical trials of an influenza vaccine, which could be a game-changer for vaccine production.
One of the biggest fears around vaccines, however unwarranted, is that they're "unnatural." Adjuvants that help improve vaccine response, such as alum, squalene, and paraffin oil, have been demonized by the anti-vaxx movement. This trend has resulted in over one-third of Americans claiming they won't get a SARS-CoV-2 vaccine when one is produced.
With over 200 vaccine trials underway, chances that 2021 will result in a reliable vaccine are high. Those worried about the "unnatural" means by which vaccines are produced may take comfort in a groundbreaking new development.
In July, Canadian biotech company Medicago began phase 1 clinical trials using a vaccine candidate that's grown in Nicotiana benthamiana, an Australian plant that closely resembles tobacco. The plant's naturally poor immune system allows virus-like particles (VLPs) to flourish. Medicago CEO Bruce Clark says the plant acts like a "bioreactor" that produces usable material in a matter of weeks.
Many vaccines are traditionally incubated in chicken eggs. The annual influenza vaccination is a common example. The process is delicate, however: US government facilities are hidden and highly secure. This method is costly, as every dose requires at least one egg. Tens of millions of chicken eggs are used for this purpose in America every year.
There's another important cost: time. While a plant-developed VLP vaccine takes roughly two months to develop, egg vaccines take up to a half-year to produce. With plants, you get a vaccine quicker and without ethical concerns for the strain on chickens.
By contrast, Nicotiana benthamiana grows in rugged environments throughout Australia. It can grow up to five feet tall. The frail leaves have made it an exceptional candidate for plant research and have been used for decades in plant virology. An experimental drug, ZMapp, developed to treat Ebola, was designed using this plant. While not without risks, the WHO claims ZMapp's benefits outweigh the risks, and has approved its usage in cocktail treatments.
Credit: alphaspirit / Adobe Stock
Clark says it's important to attack the novel coronavirus from all sides.
"Creating a sufficient supply of COVID-19 vaccines within the next year is a challenge which will require multiple approaches, with different technologies. Our proven plant-based technology is capable of contributing to the collective solution to this public health emergency."
Unlike many common vaccines, VLP vaccines contain no genetic material. You won't get infected by it, which is always a risk in live vaccines.
This SARS-CoV-2 vaccine is not the only project on Medicago's hands. The company just completed phase 3 clinical trials on an influenza. While no plant-based vaccine has been approved for use, the company hopes to replace the more cumbersome and expensive egg-based model, or at least offset some of the costs of that model. The plant model could help researchers adapt more quickly to the ever-changing influenza strains each season.
Plants offer a wonderful alternative to the current vaccination model. Besides price, VLP vaccines scale much easier and faster. If the SARS-CoV-2 vaccine works, Medicago believes they can produce a billion doses a year, by far the most ambitious yield to date. At a time when speed, cost, and reliability are all essential factors in vaccine development, we should put tobacco to better use: healing instead of harming.
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Stay in touch with Derek on Twitter and Facebook. His new book is "Hero's Dose: The Case For Psychedelics in Ritual and Therapy."
