Retinal Photoreceptors in Fossorial Tuco-Tucos (Rodentia, Ctenomys): Types, Topographies, and UV Sensitivity

PEICHL, L.; VIELMA, A.,; GLOSMANN, M.,; PALACIOS, A.,; SCHLEICH, C.E.

Congreso; ARVO Annual Meeting; 2010

The Association for Research in Vision and Ophtalmology

Abstract Purpose:Cone and rod populations in two fossorial (facultative subterranean) rodent species, Ctenomys talarum and C. magellanicus (tuco-tucos), were analyzed to elucidate whether their retinas are more adapted to their near-lightless burrows or to their occasional diurnal surface activity. Methods:Paraformaldehyde-fixed retinas were dissected and prepared as flatmounts. Overall photoreceptor densities were assessed with differential interference contrast optics. Middle-to-longwave sensitive (L) cones and shortwave sensitive (S) cones were immunolabeled by opsin-specific antisera, and their numbers and retinal distributions determined. Genomic DNA was used to PCR-amplify and sequence the tuning-relevant part of the S opsin gene. Results:C. talarum and C. magellanicus had normally developed eyes. Overall photoreceptor densities were comparatively low at 110,000-170,000/mm2. 69-85% of these were rods. However, the retinas showed high cone densities (15-31% of the photoreceptors). The majority of cones expressed the L opsin, and a 6-16% minority expressed the S opsin. No coexpression of L and S opsin was seen in any cones. L and S cones had their peak densities in mid-ventral retina and lowest densities in the retinal periphery. In C. talarum, L cone densities were 19,000-47,500/mm2, S cone densities 1,800-7,300/mm2. In both tuco-tuco species, the tuning-relevant amino acids of the S opsin indicate sensitivity in the near UV rather than the blue/violet range. Conclusions:The eyes of Ctenomys have low rod densities, similar to those of other subterranean rodents (Nemec et al, BRB 75:356, 2008). However, their cone proportions are higher than those of strongly subterranean species. Avoiding predators and selecting food during the brief above-ground excursions may have exerted pressure to retain robust cone-based vision in Ctenomys. The UV tuning of the S pigment is shared by a number of rodents, while its adaptive advantage remains enigmatic.