lunatushas a maximum binocular overlap of 100 (B). toO. lunatus. However, the ipsilateral projections to GLd and SC are 500% larger inO. lunatusthan inO. degus. Other retinorecipient structures related to ocular movements and circadian activity showed no statistical differences between species. Our findings strongly suggest that nocturnal visual behavior leads to an enhancement of the structures associated with binocular vision, at least in the case of these rodents. Expansion of the binocular visual field in nocturnal species may have a beneficial effect in light and contrast sensitivity, but not necessarily in stereopsis. We discuss whether these conclusions can be extended to other mammalian and non-mammalian amniotes. == Introduction == Among vertebrates, the Rabbit polyclonal to SLC7A5 size, shape and position of the eyes and their orbits exhibit a high degree of variability, ranging from Cyclopropavir the small, unilaterally placed eyes of the flatfishes (Achirus lineatus), to the large, highly convergent frontal eyes of humans and other apes[1],[2]. Peculiar (from a human perspective) placement of the eyes is not exceptional among fishes, perhaps reflecting the high diversity of morphological features present in these taxa. For instance, the eccentric lateral placement of the eyes of the hammerhead sharks (Sphyrnidae) endows them with a 360 span of the visual field in the horizontal and vertical dimensions, while retaining at the same time a significant amount of binocular overlap[3]. Among amniotes it is a well-established fact that convergent, more frontally oriented eyes, grant higher degrees of binocular overlap, while lateralized placement of eyes result in narrow binocular visual fields[1],[4],[5]. The degree of ocular convergence, in turn, is associated with differences Cyclopropavir in other functional aspects of the visual system, such as the presence and position of retinal specializations and the relative emphasis of the different retinal projections. In mammals, the position of the area centralis (the retinal specialization that subserves the binocular area of the visual field) varies from temporal in species with lateralized eyes to pericentral in species with frontal eyes[6][8]. Furthermore, in birds and mammals, the relative size of the visual thalamofugal projection is larger in species with frontally-oriented eyes[4],[9],[10]. In mammals the retinal ipsilateral projections to the thalamic nucleus geniculatus lateralis pars dorsalis (GLd), the visual pathway that mediates functional binocular vision, is positively correlated with the degree of binocular overlap[11][14]. Various observations show that among amniotes feeding behavior influences eye Cyclopropavir orientation. Aerial and terrestrial predators (e.g. Felidae, Strigiformes and some Caprimulgiformes) have a larger degree of binocular overlap than their prey (ranging from large herbivores to small ground feeding birds)[4],[15][17]. In addition, comparative studies indicate that irrespective of their feeding habits, nocturnal animals also exhibit a high degree of binocularity. Different taxa of nocturnal ammniotes such as the grey-headed flying fox (Megachiroptera), the Galago (Galagidae), and even the nocturnal parrot Kakapo (Strigopidae), can be cited as representative examples of this tendency[18][20]. Given these observations, enhanced binocular vision has been associated with several ecological/behavioral factors, such as nocturnality, predatory behavior and arboreal substrate. Although several comparative studies on the topic have been published[8],[15],[21][23], direct test of these ecological factors on the structural traits underlying binocular vision is lacking, likely due to the scarcity of closely related species that differ in visual abilities and life histories. Hystricognath rodents belonging to the endemic South American Octodontidae family can be considered a natural experiment, as it includes species with markedly different visual habits. The genus Octodon, endemic to central Chile, is of particular interest because it contains two closely related surface dwelling species with opposite visual habits: the diurnalO. degusand the nocturnalO. lunatus. Phylogenetic analyses suggest that these species split from a degus-like ancestor two-three million years ago (Pliocene)[24],[25]. The goal of this study is to compare the main structural features associated with binocular vision in these two closely related species. In particular, we studied the shape and position of the eyes.