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Tongue bristles help bats lap up nectar

Bumps stretch out as mammals drink

BRILLO TONGUE Rows of bristles line the tip of some nectar-feeding bats’ tongues and spring out to gather nectar when blood fills them during feeding, or when artificially pumped full of liquid, like the tongue tip shown in this scanning electron micrograph. 

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A rush of blood to the tongue helps some bats slurp up their food. Erect bristles that spring from the tongue tip of a nectar-feeding bat, Glossophaga soricina, help the bats snag sweetness from flowers, a new study finds.

As a bat reaches its tongue deep into a flower (or a manmade feeder), muscles stretch out, forcing blood from the middle of the tongue down into hairlike nubs that sprout from the tip, biomechanist Cally Harper and her colleagues at Brown University in Providence, R.I., report May 6 in the Proceedings of the National Academy of Sciences. The nubs are like water balloons that fill up when the bat feeds.

Those blood-inflated bristles grab lots of nectar quickly, making it easier for the mammals to snatch food on the fly.

Scientists had assumed the hairy bristles lining nectar-feeding bats’ tongue tips were like floppy mop strands, limply soaking up liquid. But the new study shows that the tongue bristles are actually much more active.

“It’s like if you walked into your kitchen, picked up the mop out of the corner, and the mop reached down to the floor and spread out all of its tendrils,” says biologist Margaret Rubega of the University of Connecticut in Storrs, who studies hummingbird tongues.

To see the bristles in action, Harper and colleagues stuck a high-speed video camera on a clear acrylic feeder, and rigged up fiber optics to shine bright lights on the bats’ tongues. Then the team filled the feeder with sugar water and watched as bats swooped in for the treat.

When the animals lapped up the sweet water, the sides of their glistening pink tongues turned bright red and blood-engorged bristles swelled into spikes. Like a multipronged soup ladle, the swollen spikes each pull in some nectar, Harper says.

Unlike with other mammals’ tongues, the nubs of nectar-feeding bats have adapted to the flowers the animals drink from, says biologist Alejandro Rico-Guevara, a colleague of Rubega’s at the University of Connecticut. Other nectar-feeding animals such as bees, butterflies and hummingbirds, use different strategies to suck up food, but all have evolved long tongues with special tubes, tweezers or bristles to help them drink.

The findings suggest that the honey possum, a mammal with a brush-shaped tongue tip, might also use the inflate-a-bristle technique to gather its treats, Harper says. And perhaps the bats’ tongue action could one day inspire floppy surgical tools that become firm when pumped full of air or liquid, she says.

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