To the wandering bird, bee, or insect, a flower is both a billboard and a wayfinding sign—its colors and patterning have evolved to attract pollinators and direct them towards the plant's pollen and nectar. There's one prerequisite: the visual cues require a diurnal pollinator to find the flower. What about bats, then? How do nocturnal, echolocating pollinators navigate a floral terrain? According to an article in Science, they may use acoustics. Scientists have discovered a Cuban rainforest vine with dish-shaped leaves that, in effect, communicate with bats, beckoning them to the nectar.
Hundreds of plant species are pollinated by bats. Scientists have been wondering how they attract the nocturnal animals. They noticed hemispheric curved leaves on the Marcgravia evenia plant, a vine that grows in Cuban rainforests. The leaves reflect sound waves emitted by bats more acutely than other leaves, acting as a satellite dish for bats' sonar. National Geographic reports that the curvature allows acoustically-guided pollinators to locate nectar feeders 50% faster than flat leaves.
It's the first time this type of symbiotic relationship has been discovered, and the adaptation is particularly helpful for the rare vine, M. evenia. This vine grows irregularly in the wild, according to study co-author Ralph Simon of Germany's University of Ulm, so being able to attract bats from a distance is critical for its survival. "The bats have a large range and can bring pollen to specimens which are far apart," he said. When the bat descends into the pitcher-shaped nectaries, its back brushes against the pollen that hangs above. The bat will fly off and listen for another echo emitted from the next plant's concave leaves. "The flower will receive twice as many visits and the bat will take half as long to find the flower," said research author Marc Holderied of the University of Bristol, UK.
To the plant and the bat, the leaves' design is mutually beneficial. Holderied goes on to compare M. evenia's leaves with a flower's bright colors. "What is particularly amazing about this story is that it has so much analogy to pollination by visually-oriented pollinators such as bees and birds. These visit flowers that we are so familiar with, nice and colorful. But color doesn't work at night in the rainforest and particularly it doesn't work for an echolocating pollinator."
M. evenia is just the beginning of discoveries yet to come, believe scientists. Considering the large number of bat-pollinated plants, Holderied anticipates finding "more amazing acoustic adaptation in floral signaling."