Many flowering plants are in happy, mutually beneficial relationships with animals that suck up sweet nectar from their blooms and, in exchange, carry their pollen to far-off plants, allowing them to reproduce. These harmonious relationships are the result of millions of years of specialization and co-evolution that gave all parties involved an evolutionary boost.
But the Venus flytrap (Dionaea muscipula), a carnivorous plant known for chowing down on insect, has long seemed to throw the plant-animal love-fest stereotype out the window. After all, how can a plant that’s known for eating bugs also take advantage of their help?
For a long time, this conundrum stumped biologists, but finally, in a paper published ahead of print Tuesday in the journal The American Naturalist, a team of researchers in North Carolina offer evidence that could resolve this apparent paradox. The key to understanding Venus flytrap reproduction, it seems, is in recognizing the differences between two very distinct parts of the plant: the notorious snapping jaw at its base, and the lesser-known flower towering on a stem above it.
“Before this, we knew hardly anything about pollination in Venus fly traps,” N.C. State University entomology research associate Elsa Youngsteadt, Ph.D., the first author on the new paper, tells Inverse.
By observing which gastropods, crustaceans, insects, and arachnids pollinate Venus flytrap flowers and comparing these with the prey found inside the traps, the researchers found the answer to the paradox. The bugs that pollinate the Venus flytrap are almost never the bugs that the carnivorous plant eats.
“These plants are famous, but it’s all about the traps and what they eat, and nothing about who is interacting with their flowers,” says Youngsteadt. “That’s especially interesting for this species because they’re a carnivorous plant. We know they’re eating insects, but that puts them in a potential conflict-of-interest situation that other plants can’t experience because they might be eating the same insects that might be pollinating their flowers.”
The new discovery makes the question of who pollinates Venus flytraps even more interesting. Not that scientists knew much about it before: When it came to D. muscipula pollination, there was virtually no research except a single paper from 1958 that is largely speculative and lacks observational data. Notably, though, the authors of that 60-year-old paper found that Venus flytraps were self-sterile, meaning that an individual plant had to receive pollen from a different plant to produce seeds (unlike plants like tomatoes, which can fertilize themselves). This established that the Venus flytrap needs a little help.
In their research, Youngsteadt and her colleagues from the North Carolina Botanical Garden and the U.S. Fish and Wildlife Service found that the help comes primarily from three species: the sweat bee (Augochlorella gratiosa), the long-horned beetle (Typocerus sinuatus), and the checkered beetle (Trichodes apivorus). These species were found to carry large amounts of pollen among flowers but were not found in the plants’ traps.
Spreading out their research over three sites and four different dates during the peak of Venus flytrap blooming season in Pender County, North Carolina, they came to this conclusion after catching every animal they saw crawling on Venus flytrap flowers and swabbed their bodies to examine them for evidence of Venus flytrap pollen.
Identifying the animals that were “prey” was a little grosser. “We actually pried them open gently with little forceps and pulled out whatever was inside,” says Youngsteadt. “That varied from stuff that was still alive, probably freshly caught that morning, versus things that were so digested that you can tell it was a spider but not much more than that.” For this reason, the researchers could identify only the biological family of most prey and not its species.
After identifying which animals were pollinators and which were prey, the team analyzed how many belonged to each group. Out of 54 taxa identified in flowers and traps, only 13 potential pollinators were found in the traps, and only in low numbers.
“There’s very little overlap,” says Youngsteadt. “Those species that are shared aren’t very good pollinators. They have very little pollen on their bodies, so the flytraps aren’t doing themselves any disservice.”
Laura Hamon, a student of Youngsteadt’s co-authors, Rebecca Irwin, Ph.D., and Clyde Sorenson, Ph.D., will undertake the next stage of this research: figuring out exactly how good each pollinator is at carrying pollen. This latest paper, as well as subsequent studies, will give researchers a much better idea of how to conserve the Venus flytrap, a vulnerable species that’s only found in southeastern North Carolina and northeastern South Carolina. While this latest paper doesn’t have any immediate implications, knowing more about its life cycle and ecological niche could help inform future conservation efforts for this often-poached plant.
“When you have a species that may need additional conservation management, this gem of our region, it’s important to know these basic things about its life history,” says Youngsteadt. “What does it need to live and reproduce well?”
Abstract: Because carnivorous plants rely on arthropods as pollinators and prey, they risk consuming would-be mutualists. We examined this potential conflict in the Venus flytrap (Dionaea muscipula), whose pollinators were previously unknown. Diverse arthropods from two classes and nine orders visited flowers; 56% of visitors carried D. muscipula pollen, often mixed with pollen of co-flowering species. Within this diverse, generalized community, certain bee and beetle species appear to be the most important pollinators, based on their abundance, pollen load size, and pollen fidelity. D. muscipula prey spanned four invertebrate classes and eleven orders; spiders, beetles, and ants were most common. At the family and species levels, few taxa were shared between traps and flowers, yielding a near-zero value of niche overlap for these potentially competing structures. Spatial separation of traps and flowers may contribute to partitioning the invertebrate community between nutritional and reproductive functions in *D. muscipula.
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