Nectar Feeding Bats Use Blood to Reshape Tongue for Feeding: Study

A new study by researchers at Brown University has revealed the mechanism of how bats that feed on nectar use blood flow to reshape their tongue while feeding, according to a news release.

According to lead author Cally Harper, a graduate student in the Department of Ecology and Evolutionary Biology at Brown University, bats reshape the tongue tip using blood flow to erect the hair-like structures at the right time to take in extra nectar from the flower. The study dubs the bats tongue tip as a 'hemodynamic nectar mop'.

"Typically, hydraulic structures in nature tend to be slow like the tube-feet in starfish," Harper said in a press statement. "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."

The muscle fibre present on the bats' cylindrical tongue contracts, enabling the tongue to get thinner and longer. The muscle contraction, at the same time, pushes the blood into the tiny hair-like papillae. When blood moves to the tongue tip, the papillae burst out erect, adding to the surface area and width, making the tongue function as an effective nectar-gathering device. The entire procedure of extension and retraction of the tongue tip occurs within 8 seconds.

It has long been known that the tongue of the nectar-feeding bat Glossophaga soricina is coated with tiny hair-like papillae that were considered as passive, incapable of moving on their own. These were compared to the strings on a floor mop. The researchers closely analyzed the tongue tip of the bat based on previous insights that focused on the mechanism of the hummingbirds' tongue.

During the anatomical study, Harper noticed a vascular link between the main arteries and veins of the tongue and the papillae. To check the movement of the hair-like structure, she fixed a high-speed camera on the acrylic feeder and then set up the fiber optics. This way, there would be more light on the bat's tongue. Next, the feeders were filled with sugar water. On completing this procedure, they waited for the bats to arrive.

Harper noticed that as the bats consumed the contents from the feeder, their tongues turned red and the blood-filled hair-like papillae stood erect. Each swollen papillae sucked in some nectar.

"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.

The study was published in the Proceedings of the National Academy of Sciences.