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

The golden spiny mouse (Acomys russatus), an inhabitant of rocky deserts, exhibits adaptations to diurnal activity, but also some characteristics that appear evolutionarily constrained to a nocturnal mode of life. This species is probably driven into diurnality by its congener, the common spiny mouse (A. cahirinus). We carried out a comparative study of the retinal morphology of A. russatus and A. cahirinus, in search of possible anatomical adaptations 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 microhabitat use of golden spiny mice and of illumination levels in those microhabitats. Throughout the year, golden spiny mice preferred to forage between and particularly under boulders, where light intensities were lower than in the open. Thus, the retinal structure of golden spiny mice has not evolved to meet with their needs as a diurnal species, but the combination of the biochemical properties of their eyes, coupled with their foraging microhabitat selection, may enable them to withstand diurnal activity with nocturnally adapted retinas.