High on the slopes of the Himalaya-Hengduan Mountains of southwestern China are hundreds of species of lousewort (Pedicularis) wildflowers producing special petals (galea) that resemble the heads of elephants complete with a long nose (beak). Bumblebees are their only pollinators. Multi-angle cameras recorded hundreds of video clips of bumblebee visits, revealing that the bee lands on the flower, bites the elephant’s head and shakes the muscles in her chest. The vibrations are transferred to her jaws and pollen puffs out of the elephant’s trunk. The pollen grains land on the bee’s abdomen where she gathers them up to store on baskets on her hind legs to take home to feed her larval sisters. These flowers never make nectar so pollen is the only reward and the bee cross-pollinates the flower in exchange for more baby food as she flies from plant to plant.
Figure 1: Bumblebees use vibration to forage pollen on beaked and “nosey” Pedicularis. They always bite at the base of the flower’s beak and then buzz it. The pollen released from the beak’s terminus is deposited on the bee’s abdomen. The point at which they bite produces the strongest floral vibration, discharging the most pollen from the tip of the elephant’s nose. When different lousewort species bloom together, a bumblebee will choose the flower with a beak length suitable to the length of its own winged body, resulting in a size-dependent mutualism. (Image by KIB)
To investigate why bumblebees always bite the same area on the flower regardless of lousewort species, researchers constructed a three-dimensional finite element model of Pedicularis flowers based on quantified structural and material properties of the flowers applying 3D micro-CT and atomic force microscopy.
Finite element analyses and vibrational mechanics experiments showed that, to shake the most pollen out of the elephant’s nose, there is only one “optimal biting point” on the elephant’s head located at the base part of the floral beak.
Different lousewort species produce elephant noses of different lengths and show different degrees of twisting and coiling. Bumblebees can only collect pollen and pollinate a flower in which the length of the bee matches the length of the flower from its optimal biting point through the tip of the elephant’s trunk. However, bumblebees living in the same colony change in size over the summer. That means that older and younger workers living together in the same nest may vibrate two or more different species of elephant nose flowers.
The individual-level pollination network analysis confirmed a significant "size matching" between the beak lengths of different Pedicularis flowers and the body lengths of visiting bumblebees, with precise matching observed at both species and individual levels.
This explains why you can find several different elephant nose species growing and blooming together on the same mountain slope, at the same elevation but no one has found hybrids between them. They are not sharing bumblebees of the same size and length.
“The serious challenge is to integrate biomechanics with pollination ecology as buzz pollination involves complex vibrational coupling,” said XU Yuanqing, first author and PhD. student at University of Chinese Academy of Sciences. “We successfully established a multidimensional research framework combining vibrational mechanics, insect behavior, and ecological networks.”
“What’s fascinating is that the biomechanics of each elephant nose species prevents pollen grains from reaching the wrong flower,” added Prof. Peter Bernhardt, co-author and senior pollination ecologist at the Missouri Botanical Garden. “It seems as if these flowers tell bees “Bite me here before you shake me!””
This study reveals the vibrational coupling mechanism in buzz pollination and highlights the critical role of floral biomechanics in shaping plant-pollinator interactions, offering new insights into the co-evolution of plants and pollinators and the establishment of floral diversity in wild communities over time. Given the prevalence of buzz pollination in angiosperms and its importance in some economic crops, the study offers scientific support for ecological conservation and greater management of pollination in modern agriculture.
The authors dedicate this paper to the late Professor Walter A. Macior (1936–2007), a renowned pollination ecologist who made outstanding contributions to the study of Pedicularis pollination ecology and referred to these unique species as "elephant-nose flowers." Prof. WANG Hong, corresponding author and researcher at the Kunming Institute of Botany, said “From these flowers, we read not only the wisdom of life during evolution but also the resonance of the scientific spirit across generations and international borders.
The study published in SCIENCE CHINA Life Sciences.
This research if found by The Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDB310000); The Special Foundation for National Science and Technology Basic Research Program of China (2021FY100200); The National Natural Science Foundation of China (No. 32071670).
Contact:
YANG Mei
General Office
Kunming Institute of Botany, CAS
email: yangmei@mail.kib.ac.cn
Editor:YANG Mei
