Bats' eyes adapted for both daylight and ultraviolet vision

Washington, July 28 (ANI): In a new research, s team of scientists has detected cones and their visual pigments in two flower-visiting species of bat, which has lead them to conclude that bats' eyes are adapted for both daylight and UV (Ultraviolet) vision.

The research was conducted by scientists at the Max Planck Institute for Brain Research in Frankfurt and the University of Oldenburg, in Germany.

With electroretinographic recordings, they found an increased sensitivity to UV light in cone-stimulating light conditions.

The researchers conclude that bats' eyes are adapted for both daylight and UV vision.

The UV-sensitive cones may yield a number of advantages for bats, including improved visual orientation at twilight, predator avoidance and detection of UV-reflecting flowers.

Mammalian retinas have rod photoreceptors for night vision and cone photoreceptors for daylight and colour vision.

For colour discrimination, most mammals possess two cone populations with two visual pigments (opsins) that have absorption maxima at short wavelengths (S, blue or ultraviolet) and long wavelengths (L, green or red).

The eyes of microchiropteran bats are small and their retinas are dominated by rods.

This prompted Brigitte Muller and her colleagues at the Max Planck Institute for Brain Research in Frankfurt/Main to study the photoreceptors of flower-visiting bats using histological and molecular biological methods and, with the help of Josef Ammermuller's team at the University of Oldenburg, electroretinographic recordings.

To identify the different photoreceptor types, the researchers stained the retinas of two microbat species with opsin-specific antibodies.

As expected, both species had high densities of rod photoreceptors, the prerequisite for nocturnal vision.

In addition, they were shown to possess cone photoreceptors, comprising about 2-4 percent of the photoreceptors.

"This share of cones is rather small, but from studies of other nocturnal mammals like mice we know that it allows daylight vision," said lead author Brigitte Muller.

For the two flower-visiting bats, Glossophaga soricina and Carollia perspicillata (endemic to Central and South America), the opsin labeling showed the two spectral cone types typical to mammals, the L cones and the S cones.

"The results of our study indicate cone-based UV sensitivity in phyllostomid bats," said Brigitte Muller.

"Moreover, with the two cone types, bats have the prerequisite for dichromatic colour vision, a condition common in mammals. The use of cone-based vision in addition to rod-based vision should improve the bats' capability to perceive visual information," Muller added. (ANI)