The eye in nocturnal dipsadines Atractus crassicaudatus and Sibon nebulatus (Serpentes: Dipsadinae): variations associated with lifestyle
Keywords:
Eyeball, Habitat, Natural History, Morphology, SerpentesAbstract
Snakes possess a complete eye and share similarities with other reptiles, although they present features such as the spectacle that replaces the movable eyelid. They also exhibit interspecific variations in eye size, and spectacle and corneal thickness associated with lifestyle and diel activity. We compared ocular morphology in two nocturnal dipsadine species, the fossorial
Atractus crassicaudatus and the arboreal Sibon nebulatus, using histological analyses to examine for lifestyle‑associated differences. A. crassicaudatus has smaller eyes than S. nebulatus, as well as a thinner spectacle and cornea, a very small to absent anterior chamber, a subspherical lens, and thin retinal nuclear layers. S. nebulatus has a larger eye, thicker spectacle and cornea, a distinct anterior chamber, a spherical lens, and thick retinal nuclear layers. The suite of characters in A. crassicaudatus is consistent with reduced reliance on vision in a fossorial context, whereas S. nebulatus exhibits traits compatible with enhanced visual capacity in an arboreal setting. We conclude that dipsadine snakes exhibit morphological variations in the eye, possibly associated with lifestyle, as observed here between a fossorial and an arboreal species.
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