May 7, 2013
Bats Get Tongue Erections To Soak Up Extra Nectar
Watch the video "A Dynamic Nectar Mop"
April Flowers for redOrbit.com - Your Universe Online
A new study, led by Brown University, describes the previously undiscovered mechanism used by the bat, Glossophaga soricina, to slurp up extra nectar from within a flower: a tongue tip that uses blood flow to erect scores of tiny hair-like structures at exactly the right time.
The findings were recently published in Proceedings of the National Academy of Sciences and demonstrate that the bat´s “hemodynamic nectar mop,” or tongue tip, features speed and reliability that would be the envy of industrial designers. As an example of the types of tools that nature can evolve, the tongue tip is surprising clever, according to Cally Harper a graduate student in the Department of Ecology and Evolutionary Biology at Brown University.
"Typically, hydraulic structures in nature tend to be slow like the tube-feet in starfish," Harper said. "But these bat tongues are extremely rapid because the vascular system that erects the hair-like papillae is embedded within a muscular hydrostat, which is a fancy term for muscular, constant-volume structures like tongues, elephant trunks and squid tentacles."
A mesh of muscle fibers contract the bat´s cylindrical tongue so that it becomes thinner and longer, allowing it to extend farther into the flower. The research team found that the same muscle contraction squeezes blood into the tiny hair-like papillae at the same time.
The papillae flare out perpendicular to the axis of the tongue as blood is displaced to the tip. The erect papillae add not only to the exposed surface area, but also add width. This allows the tongue to function as a highly effective nectar gathering tool.
The entire action — extension, nectar gathering and retraction — happens within an eighth of a second. Nectar feeding bats have to get a lot of calories very quickly to make the energy expenditure of hovering worthwhile.
Before this study, scientists were aware of the papillae, but regarded them as passive strings on a mop. Recent studies into the mechanics of hummingbird tongues inspired Harper to examine the shape of the bat´s tongue tip and how it is involved in nectar gathering.
Clear vascular connections between the main arteries and veins of the tongue and the papillae were observed in detailed anatomical studies. Harper was then able to recreate the erection of the papillae by pumping saline into the vascular system.
Harper said that while challenging to create, the color videos of bats feeding on nectar were especially convincing.
"That was one of my favorite parts of the study – the Aha moment," she said. "We shot color high-speed video of the bats gathering nectar, which is challenging to obtain because color cameras require a lot of light and the one thing that bats don't like is a lot of light."
Harper, with help from professors Beth Brainerd and Sharon Swartz, was able to focus a lot of light right where the tongue tip would be without shining any of the light into the bats´ eyes. This allowed the team to see that the papillae extend, they turn from a light pink to a bright red as they fill with blood.
"That was really the icing on the cake as far as nailing this vascular hypothesis," Harper said.
Harper is unsure if other nectar feeding bats have this same tongue mechanism, but the team speculates that the honey possum might also employ it. Other species, such as hummingbirds and bees, use different means of rapidly morphing their tongues for improved feeding. The researchers speculate that any or all of these highly evolved designs could provide technological inspiration.
"Together these three systems could serve as valuable models for the development of miniature surgical robots that are flexible, can change length and have dynamic surface configurations," Harper, Brainerd and Swartz wrote.
Or perhaps, we might just improve that janitor´s mop.