Visual Acuity in Mammals: Effects of Eye Size and Ecology

Abstract

Previous comparative research has attributed interspecific variation in eye size among mammals to selection related to visual acuity. Mammalian species have also been hypothesized to differ in visual acuity partly as a result of differences in ecology. While a number of prior studies have explored ecological and phylogenetic effects on eye shape, a broad comparative analysis of the relationships between visual acuity, eye size and ecology in mammals is currently lacking. Here we use phylogenetic comparative methods to explore these relationships in a taxonomically and ecologically diverse sample of 91 mammal species. These data confirm that axial eye length and visual acuity are significantly positively correlated in mammals. This relationship conforms to expectations based on theoretical optics and prior analyses of smaller comparative samples. Our data also demonstrate that higher visual acuity in mammals is associated with: (1) diurnality and (2) predatory habits once the effects of eye size and phylogeny have been statistically controlled. These results suggest that interspecific variation in mammalian visual acuity is the result of a complex interplay between phylogenetic history, visual anatomy and ecology.

Limits of Spatial Vision in Sumatran Orangutans (Pongo abelii)

“…In particular, it would be useful to compare the CSF shape, acuity, and contrast sensitivity for species specialized to habitats at extremes of light (e.g., a tropical rainforest species that encounters only filtered light versus a species that lives exclusively in bright open savanna). Our results suggest that the orangutan may not have as sensitive spatial vision as expected from considerations of eye size, phylogeny, and niche (Veilleux & Kirk, 2014). However, an answer to the question of whether the orangutan spatial vision is truly anomalous will await further behavioral studies, and anatomical assessment of the Nyquist limit of the foveal retinal mosaic and the pattern of connections between foveal cones and midget ganglion cells, the two main anatomical determinants of human visual acuity (Rossi & Roorda, 2010;Williams, 1988).…”

“…Visual acuity rather than contrast sensitivity has frequently been used as a basis for describing the visual ability of a species and for cross-species comparisons. For example, Veilleux and Kirk (2014) have described the relationship between acuity and eye size and shape, and related this to habitat considerations. However, practical as well as theoretical considerations led us to choose CS as our measure.…”

“…Primate vision shows similarities and differences across taxonomic and geographic divides as well as across habitat, life history, and ecological niche (Matsuno & Fujita, 2009;Veilleux & Kirk, 2014). For example, there are differences in color vision and visual acuity across nocturnal, diurnal, and cathemeral primates (Jacobs, 1977(Jacobs, , 1996Kirk, 2004;Matsui, Go, & Niimura, 2010;Ordy & Samorajski, 1968;Veilleux & Kirk, 2014).…”

“…For example, there are differences in color vision and visual acuity across nocturnal, diurnal, and cathemeral primates (Jacobs, 1977(Jacobs, , 1996Kirk, 2004;Matsui, Go, & Niimura, 2010;Ordy & Samorajski, 1968;Veilleux & Kirk, 2014). Eye morphology and visual system anatomy and physiology are similar within Old World monkeys and apes, but differences exist between these species and New World primates (Chan & Grünert, 1998;Waitt & Buchanan-Smith, 2006), and between haplorhine and strepsirrhine suborders of primates (Kirk, 2004;Veilleux & Kirk, 2009).…”

Plain faces are more expressive: comparative study of facial colour, mobility and musculature in primates

“…finding food and avoiding predators), may have potentiated a higher use of facial expressions that was not possible at smaller body sizes owing to physical constraints on the perception of facial movements. Facial expressions are likely more difficult to discern by smaller than larger species, because smaller mammalian eyes have lower visual acuity [18,22,23]. This rsbl.royalsocietypublishing.org Biol.…”