Researchers think a carnivorous pitcher plant uses sonar to attract bats. Why? It all comes down to poo.
A recurring pattern in Nature is that plants frequently take advantage of an animal's mobility. Whether it is to spread their seeds or to pollinate a neighbouring plant, the plant first has to attract an animal friend, which usually requires bright colours or smells (as with flowers and fruit). The pitcher plant (Nepenthes hemsleyana) on the other hand, uses sound.
|Graphical abstract from the research paper Bats Are Accoustically Attracted to Mutualistic Carnivorous Plants (M.G. Schöner et al).|
Nepenthes hemsleyana is native to Borneo, the largest island in Asia, where it feeds on any insects unfortunate enough to land in its pitcher-shaped trap. But recent research shows that the tropical plant has its eye on a bigger prize: bats.
Because bats use echolocation to navigate the forests of Borneo, they "hear" their landscape rather than seeing it, and the pitcher plant uses this to grab their attention. When the bat emits a burst of sonar, Nepenthes hemsleyana reflects the sound back to the animal in a way that is acoustically pleasing. Upon hearing the sound, the nocturnal bat takes shelter inside the plant to sleep through the daylight hours.
So why is the plant so eager for house guests if it's not actually going to eat the bat? In biology we like to say, it all comes down to poo. Like its cousins, this pitcher plant can use digestive acids to dissolve insects and absorb their nutrients, but it actually prefers bat feces. When a bat chooses to roost inside the plant for a day, it leaves behind nutritious feces which the plant considers a tasty treat. This species of pitcher plant differs from its cousins, however, because of its slender shape which is perfectly suited to reflecting the high-pitched frequency of a bat's sonar. So while other pitcher plants would love to host a bat as a houseguest, Nepenthes hemsleyana calls out “Roost here!” loud and clear.