The new study in Biology Letters reveals how the pitcher component of the Nepenthes gracilis plant is able to use falling rain as a way to catch its prey. This pitcher plant, found in Southeast Asia, is visually striking and can harness the energy of rain to ambush animals. Sometimes oddities stand out even among carnivorous plants that have evolved multiple times independently.
“This is the only case we know of where a plant actually exploits [external energy] for a purpose,” says study co-author Ulrike Bauer, an evolutionary biologist, and biomechanist at the University of Bristol in England. But how does this rain-powered trap work?
The lid of this species’ pitcher has a rigid, horizontal lower surface with an exposed underside. This surface secretes nectar, which lures insects to alight on it. When a raindrop strikes the top of the lid, the lid jerks downward and flings any unsuspecting visitor into the digestive juices below. Bauer and study lead author Anne-Kristin Lenz were able to use high-resolution x-rays to analyze cross sections when the lid was raised, lowered, and in a neutral position. They found that the lower torsional neck showed structural weakness that would result in a bobbing motion when struck by raindrops. The torsional spring made certain movements consistent with others and helped reduce springing back after being bounced off. Lastly, they found that the closely related plant Nepenthes rafflesiana lacked this mechanism because they had long necks which don’t need as much cushioning or shock absorption as short ones do.
Tanya Renner, an entomologist from Pennsylvania State University has so far, had no involvement with this research. Nonetheless, she feels that “This is a really nice study that is comparing two species and getting back to this diversity among them.” She also expressed her hope for the future work of carnivorous plants using the rain trap technique by sampling more of the extensive diversity seen in these plants. “Personally,” she adds, “I would look at more species.”
This article originally appeared in Scientific American with the title “Science in Images.” (November 2022)doi:10.1038/scientificamerican1122-26b
