Present address: Department of Biology, University of Florida, 112 Bartram Hall, Gainesville, Florida, 32611-8525, USA.
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Insights into the adaptive significance of vertical pupil shape in snakes
Article first published online: 12 JUL 2010
DOI: 10.1111/j.1420-9101.2010.02046.x
© 2010 The Authors. Journal Compilation © 2010 European Society For Evolutionary Biology
Additional Information
How to Cite
BRISCHOUX, F., PIZZATTO, L. and SHINE, R. (2010), Insights into the adaptive significance of vertical pupil shape in snakes. Journal of Evolutionary Biology, 23: 1878–1885. doi: 10.1111/j.1420-9101.2010.02046.x
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Present address: Department of Biology, University of Florida, 112 Bartram Hall, Gainesville, Florida, 32611-8525, USA.
Publication History
- Issue published online: 12 JUL 2010
- Article first published online: 12 JUL 2010
- Received 17 February 2010; revised 24 May 2010; accepted 1 June 2010
Keywords:
- activity rhythm;
- ambush foraging;
- pupil shape;
- snake
Abstract
Pupil shape in vertebrates ranges from circular to vertical, with multiple phylogenetic shifts in this trait. Our analyses challenge the widely held view that the vertical pupil evolved as an adaptation to enhance night vision. On functional grounds, a variable-aperture vertical pupil (i) allows a nocturnal species to have a sensitive retina for night vision but avoid dazzle by day by adjusting pupil closure, and (ii) increases visual acuity by day, because a narrow vertical pupil can project a sharper image onto the retina in the horizontal plane. Detection of horizontal movement may be critical for predators that wait in ambush for moving prey, suggesting that foraging mode (ambush predation) as well as polyphasic activity may favour the evolution of vertical pupil shape. Camouflage (disruption of the circular outline of the eye) also may be beneficial for ambush predators. A comparative analysis in snakes reveals significant functional links between pupil shape and foraging mode, as well as between pupil shape and diel timing of activity. Similar associations between ambush predation and vertically slit pupils occur in lizards and mammals also, suggesting that foraging mode has exerted major selective forces on visual systems in vertebrates.