Plants acoustically adapt for bats
Proving that natural adaptation knows no bounds, scientists have discovered that the dish-shaped leaves above the flowers of the vine Marcgravia evenia are designed to transmit a strong acoustic echo so bat pollinators can find the flowers.
Most small bats fly by echolocation – they emit sound and interpret the returning echoes to navigate their way around and find prey or, in the case of nectar-eaters, flowers. A team of German and UK scientists have found that, just as bright flowers serve to attracted visually guided pollinators such as birds and bees, a type of Cuban rainforest night-flowering vine has adapted to attract the Cuban nectar-feeding bat, Monophyllus remani.
The scientists were investigating why the vine had unusual dish-shaped leaf above their flowers compared to normal foliage leaves on the rest of the vine. They found that the leaf acted as an effective beacon for the bats by returning a strong, multidirectional echo from sound pulses, giving it a distinctive echo signature against the random clutter of vegetation echoes, which the visually impaired bats could home in on. Although not an acoustic adaptation, the flowers themselves also have cup-like ‘nectaries’, which are easy for the bat to feed from. These nectaries hang below a ring of flowers with protruding anthers that shed pollen, presumably all over the unsuspecting bat’s head while it sucks up some nectar.
In several experiments, the researchers found the presence of the leaves halved foraging time for nectar-eating bats. They trained three nectar-feeding bats to search for a small feeder that they attached to either a typical leaf, a dish-shaped leaf or no leaf. Next, the team measured the amount of time the animals took to find the feeders at different positions. They observed that bats found the feeders with dish-shaped leaves almost twice as fast as those without leaves or with foliage leaves.
The scientists are now on the hunt for other plant species that use “equivalent or perhaps even fundamentally different acoustic signalling to attract their bat pollinators”.
Read more about this research in Science.