Bats Follow Ultraviolet Light to Nectar, Study Suggests

John Roach
for National Geographic News
October 27, 2003

Halloween decorators take note: Reflected ultraviolet light lures bats to succulent treats. Fortunately, these bats live in the rain forests of Central and South America.

According to a team of German and Guatemalan researchers, rain forest flowers that reflect ultraviolet light may help guide the color-blind bat Glossophaga soricina to their nectar like a harbor beacon guides a ship to shore at night.

The bat's sensitivity to ultraviolet light is one facet of an evolved symbiotic relationship between the bat and the flowers. The flowers provide the bats food in the form of nectar, while the bats help pollinate the flowers, much like a honeybee, allowing the plants to reproduce.

The bats also use echolocation (akin to sonar) and the flowers' distinctive smell to find nectar-rich blooms in the rain forest, said York Winter, a biologist at the University of Munich in Germany.

Winter and his colleagues Otto von Helversen of Germany's Erlangen University and Jorge Lopez of the University of San Carlos in Guatemala reported on the ultraviolet light sensitivity of Glossophaga soricina in the science journal Nature earlier this month.

Elizabeth Dumont, a biologist at the University of Massachusetts at Amherst and member of the North American Symposium on Bat Research, said the study makes sense and may reflect a co-evolution of bats and plants.

"It is well-known that many flowers that rely on bats for pollination services are pale in color. This has been thought to make the flowers contrast with the surrounding vegetation and thus be more easily located by foraging bats. Since darkness obscures color and contrast, it makes sense that bats might use UV cues to locate flowers," she said.

Single Receptor Vision

Contrary to many fish, reptiles, birds, and insects, most modern mammals, including primates such as humans, lost the ability to see ultraviolet light over the course of evolution, according to Winter.

Most mammals are dichromatic, meaning they have the use of two types of light-receiving cells, called cones, in their eyes that allow them to distinguish two of the four primary color phases, giving them limited color resolution.

Primates, including humans, have three cones and can thus distinguish three of the primary color phases, giving us trichromatic vision, or high color resolution.

Ultraviolet vision was discovered in mammals just over a decade ago. Some rodents and marsupials, for example, can detect ultraviolet light through a distinct cone in their eyes, said Winter.

Continued on Next Page >>




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