title: Does nocturnality drive binocular vision? Octodontine rodents as a case study.
abstract: Binocular vision is a visual property that allows fine discrimination of in-depth distance (stereopsis), as well as enhanced light and contrast sensitivity. In mammals enhanced binocular vision is structurally associated with a large degree of frontal binocular overlap, the presence of a corresponding retinal specialization containing a fovea or an area centralis, and well-developed ipsilateral retinal projections to the lateral thalamus (GLd). We compared these visual traits in two visually active species of the genus Octodon that exhibit contrasting visual habits: the diurnal Octodon degus, and the nocturnal Octodon lunatus. The O. lunatus visual field has a prominent 100° frontal binocular overlap, much larger than the 50° of overlap found in O. degus. Cells in the retinal ganglion cell layer were 40% fewer in O. lunatus (180,000) than in O. degus (300,000). O. lunatus has a poorly developed visual streak, but a well developed area centralis, located centrally near the optic disk (peak density of 4,352 cells/mm(2)). O. degus has a highly developed visual streak, and an area centralis located more temporally (peak density of 6,384 cells/mm(2)). The volumes of the contralateral GLd and superior colliculus (SC) are 15% larger in O. degus compared to O. lunatus. However, the ipsilateral projections to GLd and SC are 500% larger in O. lunatus than in O. 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.
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
authors.forename: Tomas
authors.initials: T
authors.lastname: Vega-Zuniga
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
authors.forename: Felipe S
authors.initials: FS
authors.lastname: Medina
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
authors.forename: Felipe
authors.initials: F
authors.lastname: Fredes
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
authors.forename: Claudio
authors.initials: C
authors.lastname: Zuniga
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
authors.forename: Daniel
authors.initials: D
authors.lastname: Severín
authors.affiliation: Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile.
authors.forename: Adrián G
authors.initials: AG
authors.lastname: Palacios
authors.affiliation: Department of Neurosciences, School of Medicine, University of California San Diego, La Jolla, California, United States of America.
authors.forename: Harvey J
authors.initials: HJ
authors.lastname: Karten
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
authors.forename: Jorge
authors.initials: J
authors.lastname: Mpodozis
mesh_terms: D000220:Adaptation, Biological / Q000502:physiology*; D000818:Animals; D005075:Biological Evolution; D001921:Brain / Q000033:anatomy & histology; D003624:Darkness; D005123:Eye / Q000033:anatomy & histology; D005260:Female; D008297:Male; D046329:Octodon / Q000502:physiology*; D012165:Retinal Ganglion Cells / Q000502:physiology; D013045:Species Specificity; D018709:Statistics, Nonparametric; D015348:Vision, Binocular / Q000502:physiology*