Lifestyle
Forget flowers: These ancient plants attract pollinators by getting hot
Beetles (Rhopalotria furfuracea) visit a male cone of the cycad plant Zamia furfuracea, whose cones produce heat during pollination.
Michael Calonje
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Michael Calonje
Some of the earliest plants attracted pollinators by producing heat that made these plants glow with infrared light, according to a new set of experiments.
The work, published in the journal Science, suggests that long before brightly colored flowers evolved, these ancient plants would metabolically rev themselves up when they had pollen at the ready. Nocturnal insects such as beetles could then see that heat from afar and home in on the target.
These heat-producing plants, called cycads, exist today in tropical forests around the world, although they’re one of the most endangered plant groups.
“Some people call them dinosaur plants because they were much more dominant when the dinosaurs were around,” says Wendy Valencia-Montoya, a cycad expert at Harvard University.
Fossils from over 200 million years ago, compared to cycads that exist today, show that “the plants look exactly the same,” she says. “So they haven’t changed much in hundreds of millions of years.”
They’re related to pines, and male and female plants each produce fleshy, pine-cone-like structures that contain the pollen and the seeds. “That’s something very unique among this group of ancient plants,” says Valencia-Montoya, who says these are the oldest known plants that have pollen.
A couple of centuries ago, botanists noticed that these plants produced heat in their reproductive structures. Compared to the ambient air temperature, they can be hotter by 15 to 25 degrees Fahrenheit, or even more.
“We think of producing heat as something that mammals do, or birds do, but in fact, plants can do it too,” she says, although it’s not common in the plant world and takes a lot of energy.
In these plants, the heat was thought to be a byproduct of metabolic processes. Or, maybe the heat volatilized the scent of the plant, much like plugging an air freshener into an electrical outlet to generate heat that sends scent around a room. Research done in the last couple of decades has shown that male and female cones heat up at slightly different times, which could send pollinators moving from one cone to the other.
To try to understand more about what was going on, Valencia-Montoya and her colleagues painted some pollinating beetles with fluorescent markers to watch when the beetles went to the plant. And they found that the beetles were clearly going to the plant cones when they heated up.
This thermal image shows two male cycad cones releasing pollen. This plant’s cones heat up during pollen-release.
Wendy Valencia-Montoya
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Wendy Valencia-Montoya
To decouple the heat from other potential signals that these plants produce, like scent and humidity, her team used 3-D printing to make some simulated pollen cones. These fake plant structures were hollow inside, and got filled up with heated sand.
The fake cones glowed in the infrared much like real plants. “It was quite striking, when we saw it in the field,” says Valencia-Montoya, who says the fake plants were deployed outside at the Montgomery Botanical Center in Coral Gables, Florida.
Using these fake plants, the researchers figured out a couple of tricks to see if insects were attracted to the infrared glow, rather than the tactile sensation of heat itself. For example, in one experiment, they wrapped the cone with plastic wrap that is transparent to infrared light. Insects could see the infrared light but not get close enough to the cone to actually feel the heat.
What they found is that the infrared glow, by itself, was enough to attract hundreds of pollinating beetles.
And when they looked at those beetles, they found that they have specialized antennae that have evolved to detect slight differences in temperature — similar to the heat-sensing receptors used by snakes to detect prey.
What’s more, it turns out that the beetles’ antennae seem to be tuned to the exact temperature range deployed by their host plant, since different beetle species frequent different cycad species.
“Infrared radiation is perhaps the oldest discovered pollination signal,” says Nicholas Bellono of Harvard University, one of the authors of the new study.
Back when plants first evolved pollen, the insects that were around were nocturnal and had poor vision, says Valencia-Montoya. “So it makes a lot of sense that a signal like heat was guiding them.”
But as new groups emerged that were active in the day and had better vision, like butterflies and bees, “it makes more sense for plants to change their signaling strategy to also tap into the sensory systems of these more recent pollinators,” she says, adding that in evolution, there’s a constant dance back and forth between plants and their pollinators. Once color became a possible signal, flowering plants had an immense range of color combinations at their disposal, allowing them to rapidly diversify.
These researchers used “a powerhouse of techniques” to prove that the temperature of cycad’s heat-producing cones is intimately related to attracting pollinators, and that this association is ancient, says Roger Seymour, with the University of Adelaide in Australia, who wasn’t part of the research team: “This is an important contribution.”
Seymour thinks that heat could have more than one role, however, and the chance for a warm-up may be a bonus for beetles that require high body temperatures for activity. “Heat can be a direct energy reward to insect pollinators which may remain inside a thermogenic flower for much longer than insects visiting non-thermogenic species,” he says.
Irene Terry at Tthe University of Utah, an ecologist who specializes in cycads and their insect interactions but wasn’t part of this research team, says it’s only been relatively recently that people realized these ancient plants even had pollinators, rather than just spreading their pollen with the wind.
Particular odorants seem to be important pollinator attractants, she says, noting that these plants can smell like everything from bubblegum to bell peppers. Still, this study shows “in the most beautiful way” that infrared is also key.
“I was not surprised at all that infrared was involved,” says Terry, given that other insects like mosquitoes use infrared to find their way to a target. “There’s a range of things that insects can see that we don’t.”
Imagine, says Bellono, being a prehistoric beetle trying to navigate the darkened environment in the early evening, and seeing various plants start to glow red.
“The infrared is an entirely different world that we don’t experience,” he says. “I think that’s a cool thing to think about, going back in time, that this signal was around when the dinosaurs were there, long before us. And the beetles still use it to this day and are still experiencing that world.”
Can you say no to a friend’s wedding?
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Are we spending too much on other people’s weddings?
Going to a friend’s weddings can be so fun and meaningful… but it can also really hurt your wallet. A survey by LendingTree found that 31% of people who had been to a wedding in the past five years had accrued debt to attend. So what’s driving up the cost of weddings for guests? And what makes it so hard to say no to these expenses?
Brittany breaks it down with Allyson Rees, senior analyst at trend forecasting firm WGSN, and Annie Joy Williams, assistant editor at The Atlantic.
This episode was produced by Liam McBain, with additional support from Corey Antonio Rose. It was edited by Neena Pathak. Our Supervising Producer is Cher Vincent. Our Executive Producer is Barton Girdwood. Our VP of Programming is Yolanda Sangweni.
After the eight-day-long fire in a 500,000-square-foot Boyle Heights warehouse, eastern Los Angeles residents are contending with putrid smells, soot and potentially hazardous airborne chemicals after heavy plumes of smoke spread throughout the city. But those who grow food in nearby neighborhoods may also be wondering: How will the fires affect the plants and produce in my garden?
The Boyle Heights warehouse, owned by Lineage — a global temperature-controlled storage facility operator — housed 85 million pounds of frozen food and other products. In the days since the fire, local emergency visits for smoke inhalation and throat pain spiked while agencies still scramble to measure the amount of PM 2.5 — harmful fine particles — and heavy metals, like lead and arsenic, in the air.
According to researchers, any toxic airborne chemicals would likely stem from the charred foam insulation, metal exterior, burned solar panels and any lithium batteries that might have been present inside the warehouse.
After a fire, heavy metal particles can spread through ash and smoke over gardens and inhibit growth, said Olukayode Jegede, an agricultural toxicologist and assistant professor at UC Davis. Since the warehouse fire is so recent and cleanup has just begun, Jegede said the precise impact on gardens can’t be measured until comprehensive soil tests are conducted in the area.
While the L.A. city government hasn’t announced plans for soil testing, the Contaminant Level Evaluation and Analysis for Neighborhoods project at USC is offering free contaminant testing for Boyle Heights and East L.A. residents. Residents can collect soil samples and deliver them to Boyle Heights City Hall and other locations for an evaluation of lead, arsenic, chromium and mercury levels.
The good news is produce, plants and roots can still be preserved. According to Jegede, many of the soil tests conducted last year in the Altadena area after the Eaton fire showed that gardens and poultry were not as contaminated as one might expect.
“Quite a number of the soils we tested [in Altadena] were not really contaminated,” Jegede said. “We weren’t seeing many soils with concerning elevated levels of metal, so gardeners should not be too alarmed when these things happen.”
Nevertheless, there are several measures that gardeners can take to keep themselves, their children, plants and produce safe from potentially harmful contaminants stemming from the fire. Researchers, gardening experts and horticulturists offered some guidance on the handling, recultivation and cleanup that can keep you and your garden in good health.
How do I remove ash and contaminants from my garden?
Altadena horticulturist Leigh Adams said Boyle Heights plants and produce already live in a difficult environment, surrounded by industrial warehouses that spread contaminants daily.
“That area has been used industrially for 100 years, and the soil is impacted by many, many, many things,” Adams said. “Low-income neighborhoods and gardens usually don’t have a lot of resistance against dominant manufacturing.”
This means that the contamination of gardens in eastern L.A. won’t be as catastrophic as compared with those in Altadena, a more suburban environment, Adams said. But fallen ash still poses major health risks if ingested or inhaled.
An advisory from University of California Agricultural and Natural Resources last year recommended suiting up in an N95/KN95 mask, long sleeves, pants, close-toed shoes and gloves before attempting to deal with ash in the garden to limit exposure to potentially toxic contaminants. The advisory added that individuals should make sure all of this gear is cleaned thoroughly before bringing it back inside.
Once in the proper gear, Adams recommends removing the top two inches of topsoil from gardens, where the highest concentration of contaminants will settle after a fire. Using a plastic bag to collect the soil and disposing of it in the garbage — not green yard waste bins — will help to reduce the spread of airborne chemicals.
Gardeners with raised beds are advised to remove approximately six inches of soil, because excess ash can raise the pH level and prevent nutrients from soaking into the soil bed.
After this, watering the garden gently but plentifully will help to promote soil health and get rid of most of the ash present on plant leaves and stems. Adams said replacing the top two inches of soil with store-bought mulch or straw will help to contain any remaining ash and prevent it from spreading any further.
Experts say to avoid using leaf blowers if ash is present in the garden because they can send particles airborne. Doing so will increase the likelihood of heavy metal particles, which can carry lung irritants and carcinogens, being spread and inhaled.
A Boyle Heights resident keep a watchful eye on the fire at the 5,000-square-foot commercial building, which stores 85 million pounds of frozen food.
(Genaro Molina / Los Angeles Times)
Is it safe for me to eat produce from my garden?
Several studies, including one from the UC Cooperative Extension of Sonoma County, have shown that consuming produce in a fire-affected area poses minimal health risks.
Jegede said most root vegetables like potatoes and carrots, along with any fruit that has an outer layer, can be washed to remove potential contaminants, even if they were covered in ash. Peeling the outer layer of your produce can also help to reduce potential risks, he said.
Lettuce and other leafy foods with multiple layers pose a higher risk of contamination, but with a vigorous wash and peeling the outer layers, even the greens can be saved. The County of Los Angeles Department of Public Health recommends soaking leafy produce and fuzzy fruits like peaches in a 10% white vinegar and 90% water mixture.
Jegede said if the leaves or fruit are too delicate to wash or ash is still visible, it would be best to dispose of the produce.
How can I tell if my soil is contaminated?
After ridding your garden of visible ash, you might wonder how to tell if your plants will still thrive in the soil.
At-home soil tests that measure for alkaline, fertility and pH levels are widely available and can be purchased for $15 to $100 (for more detailed results) online. But Jegede said these tests can’t tell the full story of soil health.
Comprehensive soil testing is “something you can’t do properly at home,” Jegede said. “In labs, we are testing for metals like lithium and zinc, stuff that an at-home test will not show … If it comes to the point that you’re worried about your soil, I would just send it out to a lab.”
Wallace Laboratories in El Segundo, Babcock Laboratories in Riverside, Waypoint Analytical in Anaheim and other labs offer more detailed soil tests that measure heavy metal particles in addition to other fertility factors. Prices at Wallace Laboratories can range from $115 to $295 for a complete compost test.
The soil below two inches should be unharmed, Adams said, so long as new compost is set and plants are watered plentifully, which will promote natural biological cycles.
“What you’re doing is capping the soil, so that moisture stays in there, and instead of being dirt, it’s a living system called soil,” Adams said. “The more carbon we can get into our soil, the better.”
What can I do to help my soil recover?
For the last 12 years, Adams has been working with Metabolic Studio, a Los Angeles-based art and research hub focused on environmentalism, on methods for bioremediation, the practice of using additional fungi, plants and compost to decontaminate ash and break down contaminants.
Adams said straw, mushrooms, corn, rye and sunflowers are great bioremediators that can help to repair damage to soils. She said certain samples she’s worked on with Metabolic Studio have gone from testing at high heavy metal levels to nearly contaminant-free.
But for a more immediate fix, wash your produce, water your plants and have a little patience during ash cleanups. Your garden should look better in no time, Adams and Jegede said.
Inde Navarrette and Michael Johnston in Obsession.
Focus Features
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Focus Features
Two big horror films, Obsession and Backrooms, just smashed all box office expectations. So much of their success has been driven by Gen Z, which is now the biggest moviegoing demographic. But what makes a movie a Gen Z movie? Today we’re bringing you an episode of NPR’s It’s Been a Minute. Host Brittany Luse talks about this trend with Sam Adams and Reanna Cruz.
If you want to hear more about these movies, check out these episodes:
In ‘Obsession,’ love hurts. It really, really, really hurts.
‘Backrooms’ brings YouTube horror to the big screen
Zendaya brings ‘The Drama,’ we bring the spoilers
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