Ground Squirrels (Spermophilus Dauricus) Study, As The Structure And Distribution Of Photoreceptor Cells

Spermophilus dauricus is a seasonal hibernating animal, which widely distributed in the north, northwest and northeast of China. It is belong to Sciuridae genus Spermophilus. It’s a typical diurnal rodent. In attempt to clarify whether it is able to distinguish different spectrum and whether has color vision. There are many biological technology and methods, such as histology and immunofluorescence, which will be applied in this project to study the visual system and the topography of photoreceptors in the retina of the Spermophilus dauricus. It is concluded that1. The shape and structure of the eye in Spermophilus dauricus is normal, possess the basic structures:eyelid、cornea、iris、lens、choroid layer and retina. The major macroscopic feature of the Spermophilus dauricus retina is a linear optic nerve head. It is oriented horizontally across the central superior (dorsal) portion of the posterior pole. This structure served as the principal topographical landmark in our study.2. Spermophilus dauricus with a large number of photoreceptors and ganglion cells in the retinas, The thickness and shortness of photoreceptor layers is almost similar to the ganglion cells layers. It illustrated that Spermophilus dauricus is adaptive to relatively high levels of light. The thickness of the retinal pigment epithelium is relatively uniform, with no discernible topographic. It will protect the retina in Spermophilus dauricus, preventing the damage to the photoreceptors when exposed to relatively high lelves of light.3. Within the retinas of Spermophilus dauricus, there is thickness asymmetry between the temporal and dorsal, such as inner nuclear layer, inner plexiform layer and ganglion cells in the retinas. It suggested that this asymmetry may be related to surface-dwelling habitats.4. Spermophilus dauricus has two classes of cones, a majority of M/L-cone,and a minority of S/UV-cones. It indicated that the Spermophilus dauricus was a typical dichromatic color vision. This rodent can apparently make some color discriminations. The distributions of cone photoreceptors have been determined in the retina of the Spermophilus dauricus, The peak density for the M/L-cones about32,685/mm2is found in a horizontal strip of central retina2.5mm ventral to the elongated optic nerve head, falling gradually in the dorsal and ventral retinal periphery, the M/L-cone distribution showed a dorsoventral asymmetry with higher densities in the central area than in the periphery area. The density of value in the nasal is slightly higher than the temporal, and with higher densities in the ventral area than in the dorsal area, at the extreme dorso-nasal retinal margin the density of value are5580mm2. S/UV-cone density is far less than M/L cone. S-cone density is relatively flat across most of the retina, reaching a peak5394/mm2at the central retina, falling gradually in the dorsal and ventral retinal periphery. The S/UV-cone distribution showed a dorsoventral asymmetry with slightly higher densities in dorsal than in ventral retinal regions. M/L-cones and S/UV-cones yielding a ratio of about13:1. Suggesting that Spermophilus dauricus retinas are extremely M/L-cone-dominated. These features are accordance with the characteristics of the typical diurnal animals.5. Rods are only existent in the periphery retina. The rods achieve29%of the local photoreceptor population10,000/mm2in the ventral retina. Rod density is low in the dorsal, where the rods comprise less than4%of the local photoreceptor population, the density roughly2000-3000/mm2.By contrast, the change in rod/cone ratio between the dorsal and ventral halves of the retina indicates a conspicuous asymmetry in the Spermophilus dauricus’s visual system. Suggesting a specialization for maximizing visual sensitivity under dim levels of illumination in the superior visual field. Rod play an important role under dim levels of light conditions.In summary, the visual organ in Spermophilus dauricus is adaptive to long term surface dwelling habitat, this rodent can apparently distinguish the different spectrum and make some color discriminations. However, whether and how Spermophilus dauricus might exploit color vision in their normal environments remains an open question.