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Pitchers of Sarracenia, found in the bogs of eastern North America, resemble trumpet-shaped flowers, often in purplish or reddish hues. But appearances can be deceiving. The striking “flowers” are actually modified leaves, forming a cup that contains digestive enzymes.
When a small animal – usually an insect – gets too close, the pitcher functions as a pit trap, with slippery sides that prevent the critter from climbing up. The carnivorous plant then digests the insect, obtaining food that may be difficult to obtain from the nutrient-poor soil in its swampy home.
Different types of Sarracenia pitchers tend to eat different types of insects – some species trap more ants, while others feast on bees and moths. The color, size or shape of the pitcher could play a role in the ability of plants to attract prey, according to different hypotheses put forward by scientists. A new study, published Wednesday in the journal PLOS ONE, points to another weapon in the pitcher plant arsenal that could help explain the diets of different species: smell.
Dr. Laurence Gaume, lead author of the study and researcher at the CNRS and the University of Montpellier, has been studying carnivorous plants for more than 20 years.
In previous work on Southeast Asian pitcher plants, which are only distantly related to the North American Sarracenia, she and her colleagues found that different species also captured different proportions of ants to flying insects. The research team learned that the odors emanating from the different species of Asian pitcher plants attracted different types of insects. She therefore wanted to see if the same was true for North American pitcher plants.
For us humans, it’s difficult to distinguish the subtle differences in odor from one Sarracenia species to another, especially, Gaume said, when the plants’ characteristic odors are dominated by their meals.
“The smell of rotting organic matter…can be strong in pitchers full of bugs,” she said. But recently opened pitcher plants that don’t stink of rotting insect carcasses provide an opportunity to identify odors, she explained.
“We can note different smells depending on the species, which range from the smell of green grass to floral or even fruity smells.”
These odors are caused by volatile organic compounds, or VOCs, produced by plants. In the new study, Gaume and colleagues, including Corentin Dupont, a CNRS and University of Montpellier doctoral student and first author, selected four types of Sarracenia pitcher plants (two found in nature and two man-made hybrids). and examined the VOCs they produce.
The study team placed each plant in an airtight bag and pumped purified air through it. The molecules responsible for the odors produced by the plants were trapped on filters for the researchers to analyze and identify. The team found that the different species of pitcher plants each produced their own unique bouquet of VOCs.
Dr Claire Villement, an entomologist at the National Museum of Natural History in Paris and co-author of the study, examined the insects caught by 41 pitchers of the four species in the study. While the pitchers contain digestive enzymes that break down insect bodies, Gaume explained that it is safe for humans to handle the pitchers and their partially digested prey: “There is no danger, the enzymes cannot not eat your hands.
As expected, the different pitcher species trapped different types of insects.
The researchers then compared the VOCs produced by each plant with the types of insects it caught. Species that produced more floral scent caught more bees, moths, and other flying insects; pitchers that produced more fatty acids caught more ants. These results held even when the researchers took into account how the size and shape of the pitchers could limit the types of insects they could easily trap.
Gaume was careful to note that the study does not definitively prove that these different scents attract different types of insects; it just shows a strong correlation. Still, it makes intuitive sense that pitchers that smell like flowers might attract pollinators flying from bud to bud, while ants, which rely heavily on chemical cues from fatty acids, might gravitate toward those smells.
“These findings are important because they suggest that these carnivorous plants are not just passive plants with random catches, and that they can target their prey,” Gaume said.
Dr Aaron Ellison, a retired principal investigator at Harvard Forest in Petersham, Massachusetts, who was not involved in the project, said: “This is an interesting study. I think the conclusions they come to are solid with the data they have. The biggest challenge with the study, honestly, is that they did it in France,” rather than the native North American bogs of the Sarracenia plants.
He also noted that the study features horticultural varieties in addition to wild plants, which may behave differently. “I would love to see this kind of work done in the field in the southeastern United States with plants growing in their normal habitat,” he said.
These natural habitats are under threat due to the climate crisis, pollution and land development, said Dr. Phil Sheridan, president and director of the Meadowview Biological Research Station in Woodford, Virginia.
He was not involved in the study, but hailed it as “a key paper” providing “compelling evidence” that the pitcher plants’ scents, as well as their physical structures, influence the insects they are able to attack. catch. It is important to study pitcher plants because of the unique role they play in their increasingly fragile ecosystems, he added.
“They grow in very sensitive habitats, the water is very clean where they grow and if you pollute it, it’s over. It’s over,” Sheridan said. “These are beautiful plants, and once they’re gone, you don’t get them back.”
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