Newly found plant works with sonar to attract bats | Environment | All topics from climate change to conservation | DW | 29.07.2011

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Newly found plant works with sonar to attract bats

All is dark at night. So how can a plant attract pollinators – specifically, bats? Researchers writing in Science magazine report that a Cuban rainforest plant has evolved a clever solution: Acoustically-shaped leaves.

bat approaching plant

A rainforest plant has evolved to attract bats

Most plants are pollinated through bees, but one plant, Marcgravia evenia, which grows in the Cuban rainforest, has it a little harder: it has to attract on-the-go bats in the dark of night.

Instead of using their eyes, the flying mammals orient themselves with echolocation: they send out ultrasound waves and listen closely to which sounds echo back.

According to a study published Friday in the journal Science, a team of British, German and Canadian researchers have shown that this newly-discovered plant that has evolved to reflect back especially audible ultrasound waves. Marcgravia evenia achieves this through concave, spherically shaped leaves.

A steady response

plant with leaf and flower

Cuban rainforest plant Marcgravia evenia

Concave hemispherical shapes are particularly easy for bats to find in the dark, according to Ralph Simon, an Ulm University biologist, and co-author of the paper.

"That's why we weren't particularly surprised when we found this plant in Cuba, which presents with spherically formed, large leaves above its blossoms," Simon told Deutsche Welle.

"By night, we observed bats at these blossoms, which went totally crazy over the large amount of nectar there," he said.

The scientists measured the sound reflection of the dish-like Marcgravia evenia leaves and found that indeed, the echo from there is louder. Moreover, the research team found that the echo remains at the same volume even when the bat changes its position.

Regular, flat leaves, such as those on other plants in the rainforest, only bounce back strongly audible echoes when the wave hits them at a specific angle. If the animal moves one degree left or right, its echo response is faded.

The hemispherical leaves, through their form, maintain "a different sound form from the surrounding vegetation, through which their blossoms become more conspicuous," Simon added.

Benefits all around

man in rainforest

Ulm University researcher Ralph Simon in the Cuban rainforest

In the laboratory, Ralph Simon and his colleagues were able to reproduce just how this trick works: In an artificial forest, bats found a feeding array in thick foliage twice as fast when a replica of a dish-shaped Marcgravia evenia leaf was brought into play.

Within 12 seconds, the bat arrived at its goal, whereas without the hemispherical guides, it needed 23 seconds.

If the feeding array was fitted with a flat, regular leaf, the search, at 22 seconds, lasted nearly as long as with nothing.

"This echo beacon has benefits for both the plant and the bats," said Marc Holderied, a biology lecturer at the University of Bristol, in the United Kingdom, in a statement. Holderied was also one of the paper's co-authors.

"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 fulfill their energy needs," he said. "On the other hand, the M. evenia vine occurs in such low abundance that it requires highly mobile pollinators."

Autorin: Brigitte Osterath / sad
Redaktion: Cyrus Farivar

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