Eye morphology in some wild rodents.

The eye anatomy of six rodent species (Murinae: Apodemus sylvaticus, Mus domesticus, and Mus spretus; Arvicolinae: Clethrionomys glareolus, Arvicola terrestris and Microtus arvalis) was compared by means of light or electron microscopy to determine adaptive, and evolutive signals. Our observations revealed inter-specific morphological differences, which were moderate among representatives of the same subfamily. Specifically, traits that distinguished murines from arvicolines were the globe's relative size, the pupillary constrictor muscle, the amount of retinal epithelium melanin, and the thickness of certain ocular coats. Moreover, adaptations to new habitats and differences in temporal activity among species of the same subfamily determined discords respect to the phylogenetic patterns. This was true of the adaptations to underground conditions seen in A. terrestris, which involved the thickness of the cornea, sclera, and choroids. Likewise, A. sylvaticus had adaptations to its nocturnal lifestyle, as shown by the large overall size of the eye and lens, and by a large, thick cornea.