Retinal Photoreceptors of Two Subterranean Tuco-tuco Species (Rodentia, Ctenomys): MorphologyTopography, and Spectral Sensitivity

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

JOURNAL OF COMPARATIVE NEUROLOGY

WILEY-LISS, DIV JOHN WILEY & SONS INC

Año: 2010 vol. 518 p. 4001 - 4015

0021-9967

Traditionally, vision was thought to be useless for animalsliving in dark underground habitats, but recent studies in arange of subterranean rodent species have shown a largediversity of eye features, from small subcutaneous eyes tonormal-sized functional eyes. We analyzed the retinal photoreceptorsin the subterranean hystricomorph rodentsCtenomys talarum and Ctenomys magellanicus to elucidate whether adaptation was to their near-lightless burrows orrather to their occasional diurnal surface activity. Bothspecies had normally developed eyes. Overall photoreceptordensities were comparatively low (95,000–150,000/mm2 in C. magellanicus, 110,000–200,000/mm2 in C. talarum), and cone proportions were rather high (10–31%and 14–31%, respectively). The majority of conesexpressed the middle-to-longwave-sensitive (L) opsin, and a 6–16% minority expressed the shortwave-sensitive (S)psin. In both species the densities of L and S cones werehigher in ventral than in dorsal retina. In both species thetuning-relevant amino acids of the S opsin indicate sensitivityin the near V rather than the blue/violet range.Photopic spectral electroretinograms were recorded.Unexpectedly, their sensitivity profiles were best fitted bythe linear summation of three visual pigment templateswith kmax at 370 nm (S pigment, UV), at 510 nm (L pigment), and at 450 nm (an as-yet unexplained mechanism).Avoiding predators and selecting food during the briefaboveground excursions may have exerted pressure toretain robust cone-based vision in Ctenomys. UV tuning of the S cone pigment is shared with a number of other hystricomorphs. J