Abstract
Purpose::
The microchiropteran bats are strongly nocturnal, with small eyes and heavily rod dominated retinae. However, they also possess significant cone populations and hence the basis for daylight vision and color vision (Müller & Peichl, IOVS 46: E-Abstract 2259, 2005). Here, we have analyzed the cone types and cone densities, and assessed the spectral tuning of the shortwave sensitive (S) cone opsin, in the nocturnal flower bat Glossophaga soricina (Phyllostomidae). In behavioral experiments at dark-adapted (rod stimulating) conditions, G. soricina was able to detect ultraviolet stimuli but could not be trained to discriminate between colors (Winter et al., Nature 425: 612-614, 2003). We were interested to see whether the cones could also confer UV sensitivity.
Methods::
Adult animals came from our breeding colony. Eyes were enucleated directly post mortem. In paraformaldehyde-fixed retinae, middle-to-longwave sensitive (L) cones and S cones were assessed using cone opsin specific antisera. Retinal cDNA and genomic DNA were used to PCR-amplify and sequence the tuning-relevant part of the S opsin gene.
Results::
G. soricina possesses L and S cones. Across the retina, cone densities range from 4000/mm² to 7000/mm², with a regionally varying majority of 60-80% L cones and a minority of 20-40% S cones (relatively high compared to other mammals). G. soricina is identical to mouse in the amino acids that have been shown to tune the mouse S opsin to UV rather than blue.
Conclusions::
The cones may be useful for visual orientation at dusk and dawn. The presence of two spectral cone types provides the basis for dichromatic color vision, including the detection of UV light, in cone-stimulating light conditions. Opsin gene analysis indicated the presence of an L opsin and a UV-tuned S opsin also in the vespertilionid bat Myotis velifer (Wang et al., Mol. Biol. Evol. 21: 295-302, 2004). This is different from most eutherian mammals where the S opsin is tuned to blue.
Keywords: retina: distal (photoreceptors, horizontal cells, bipolar cells) • photoreceptors • opsins