Retinal structure and foraging microhabitat use of the golden spiny mouse (Acomys russatus)

The golden spiny mouse (Acomys russatus), an inhabitant of rocky deserts, e xhibits adaptations to diurnal activity, but also some characteristics that appear evolutionarily constrained to a nocturnal mode of life. This specie s is probably driven into diurnality by its congener, the common spiny mous e (A. cahirinus). We carried out a comparative study of the retinal morphol ogy of A. russatus and A. cahirinus, in search of possible anatomical adapt ations for diurnal activity in the eyes of golden spiny mice. The observed photoreceptors of both species had rod-pattern properties that characterize nocturnal mammals. We also carried out a field study of the foraging micro habitat use of golden spiny mice and of illumination levels in those microh abitats. Throughout the year, golden spiny mice preferred to forage between and particularly under boulders, where light intensities were lower than i n the open. Thus, the retinal structure of golden spiny mice has not evolve d to meet with their needs as a diurnal species, but the combination of the biochemical properties of their eves, coupled with their foraging microhab itat selection, may enable them to withstand diurnal activity with nocturna lly adapted retinas.