Leaf acts as an echo beacon to lure bat pollinators

By Yun Xie



As a Pallas’s long-tongued bat flies around a rainforest looking for nectar, it relies on echolocation from the sound it emits to find flowers. From a plant’s perspective, it's good to be found by bats, which are highly mobile pollinators. But how can a plant stand out among the sea of foliage in a rainforest?

A recent paper in Science reveals that the vine Marcgravia evenia from the Cuban rainforest has evolved to catch a bat's attention by producing one to two dish-shaped leaves near its flowers. These dish-shaped leaves stand upright and point the concave side toward nectar-feeding pollinators. The dimensions of the leaves make them an acoustic beacon for bats.

The dish-shaped leaves (51mm x 35mm and 13mm deep) are quite different from typical floral leaves (74mm x 28mm, 3mm deep), and this difference translates into drastically different echo properties. The relatively flat foliage leaf produces the strongest echoes directly from the front, but the echo strength tapers off significantly as you move away laterally. In contrast, dish-shaped leaves have strong echoes that stay pretty consistent across a 120° arc. This means that the echo of dish-shaped leaves can be detectable within a volume of roughly 25m3, compared to 15m3 for foliage leaves.

The echoes from dish-shaped leaves would also have an acoustic signature that's distinct from background foliage echoes. The echo impulse responses, as measured by a biomimetic sonar head, show that the echoes from dish-shaped leaves do not vary spatially. That is the echoes barely change in amplitude and frequency over a wide range of directions. This should make the dish-shaped leaves stand out to passing bats, as echoes from foliage leaves vary drastically with direction change.

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http://arstechnica.com/science/news/2011/07/leaf-acts-as-an-echo-beacon-for-bats.ars