Meeting Abstract
Visual adaptations such as eye size (i.e. eye diameter), acuity (the ability to discern detail), sensitivity (the amount of light needed for image formation), and pupil shape can be used to infer the relative importance of vision to an organism. Eyes and the visual processing system are metabolically costly to maintain, suggesting that large relative eye size (as it relates to body length) may have a significant ecological or evolutionary role, such as mate selection, predator avoidance, and foraging strategy. Elasmobranchs comprise a morphologically diverse group that has successfully filled a wide range of marine and freshwater niches. Several species occupy different predatory niches across their lifetime as their energetic and ecological demands shift, yielding a wide range of visual habitats. As eye size changes with body length ontogenetically, they represent an ideal group for examining scaling relationships, such as eye growth rate (i.e. slope) and eye size at a given body length (i.e. intercept) within the context of visual habitats. In this study, we quantified the relationship of eye size and body length in 6 species of sharks and compared this scaling across species that differ in ecological lifestyle (i.e. activity level, habitat, and maximum size). Eyes of all species scaled hypoallometrically with body size, however larger and more active species (e.g. the white shark Carcharodon carcharias) had larger relative eye sizes than smaller, less active species (e.g. the Atlantic sharpnose shark Rhizoprionodon terraenovae). Larger eyes for active predators may provide either greater sensitivity or greater visual acuity which would enable these species to carry out visually-guided behaviors across a wide range of visual habitats.
