Plant lures bats with echoing leaf

Scientists discover a Cuban rainforest vine with leaves shaped to attract nectar-feeding bats

Flowers use bright colours and striking patterns to attract pollinators that are guided by sight, such as bees and hummingbirds. So it makes sense that plant species pollinated by bats, which are guided by sound, should entice them in a similar way.

Now scientists from the UK and Germany have proved the point for the first time. They have discovered a Cuban rainforest vine – Marcgravia evenia – that grows a dish-shaped leaf just above each flower, to send back conspicuous echoes to nectar-feeding bats. As a result, the bats find its flowers twice as fast by echolocation as they would otherwise.

By analysing the leaf’s acoustic reflection properties, the researchers found that it acts as an ideal beacon, sending back strong, multidirectional echoes with an easily recognisable acoustic signature – perfect for making the flower obvious to echolocating bats.

The scientists then trained nectar-feedingGlossophaga soricina bats to search for a single small feeder hidden within an artificial foliage background, varying the feeder’s position and measuring the time the bats took to find it. The feeder was presented on its own, or with a replica of either an ordinary foliage leaf or the distinctive dish-shaped leaf. Search times were longest for all bats when the feeder was presented on its own, and were very slightly shorter when a foliage leaf was added. However, a dish-shaped leaf placed above the feeder always reduced the bats’ search times – by around 50 per cent.

Although the leaf’s unusual shape and orientation mean that it is less efficient at photosynthesis than an ordinary leaf, the cost is outweighed by the benefits of more efficient pollinator attraction. The leaf and its flower stand out from the chaotic stream of echoes being reflected back to squeaking bats from nearby rustling plants.

“This echo beacon has benefits for both the plant and the bats,” says Dr Marc Holderied of Bristol University, a co-author of the study, published in the journal Science. “On one hand, it increases the foraging efficiency of nectar-feeding bats, which is of particular importance, as they have to pay hundreds of visits to flowers each night to fulfil their energy needs. On the other hand, the Marcgravia eveniavine occurs in such low abundance that it requires highly mobile pollinators.”

Bats, with their wide home range and excellent memory, are efficient pollinators and many other tropical plants depend on them. As the acoustic and perceptual principles shaping the echo beacon leaf of Marcgravia evenia should work for all echolocating pollinators, the researchers expect to find other instances of plant species that use acoustic signalling to attract their bat pollinators.