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Conquering the cold shudder: the origin and evolution of snake eyes

Caprette, Christopher L
http://rave.ohiolink.edu/etdc/view?acc_num=osu1111184984

Abstract Details

2005, Doctor of Philosophy, Ohio State University, Evolution, Ecology, and Organismal Biology.
I investigated the evolutionary origin and diversity of snakes by examining one complex structure, the eye. Using light and transmission electron microscopy, I contrasted the anatomy of the eyes of diurnal northern pine snakes and nocturnal brown treesnakes. Among the observed differences, brown treesnakes have much larger lenses than those of northern pine snakes for similar sized eyes. Northern pine snakes have a simplex, all-cone retina, while brown treesnake retinas have both rods and cones. The cone ellipsoids of northern pine snakes contain microdroplets that act as light guides, and there were similar droplets in brown treesnake rods, although their function is not clear. The density of photoreceptors and neural layers in brown treesnake retinas predict that brown treesnakes should have the same visual acuity under scotopic conditions that northern pine snakes have under photopic conditions. Next, I quantified orbital area, binocular overlap, eye size, lens size, and the refractive powers of the lens and spectacle among colubrid and crotalid snakes. The size-adjusted orbital area fit preditions based upon ecology, but binocular overlap did not for colubrid snakes. Pit vipers had much smaller orbital areas than colubrid snakes, but significantly greater binocular overlaps. The eastern cottonmouth, an aquatic pit viper, had a much greater average orbital area than its body size predicted, which may be due to its unique ecology. The eyeballs of both colubrids and pit vipers were significantly subspherical, as were the lenses of several species, and the lens contributed significantly more to the total refraction than the spectacle in all but one species, the brown treesnake, in which the spectacle had greater refractive power. Lastly, snakes evolved from lizards, but their eyes are substantially different. I compared the anatomy of vertebrate eyes across many taxa to evaluate alternative hypotheses concerning the evolution of the distinctive features of snake eyes. My analyses retrieved groupings consistent with ecological adaptation rather than accepted phylogenetic relationships. Moreover, snakes clustered with primitively aquatic vertebrates, whereas fossorial lizards and mammals clustered together. Those results support the hypothesis that snakes evolved from aquatic ancestors.
Thomas Hetherington (Advisor)
107 p.
Serpentes; Snakes; Eyes; Evolution; Morphology; Adaptation

Recommended Citations

Citations

  • Caprette, C. L. (2005). Conquering the cold shudder: the origin and evolution of snake eyes [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1111184984

    APA Style (7th edition)

  • Caprette, Christopher. Conquering the cold shudder: the origin and evolution of snake eyes. 2005. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1111184984.

    MLA Style (8th edition)

  • Caprette, Christopher. "Conquering the cold shudder: the origin and evolution of snake eyes." Doctoral dissertation, Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1111184984

    Chicago Manual of Style (17th edition)

osu1111184984
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© 2005, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.