Meeting Abstract
Adaptations of visual systems, such as acuity, sensitivity, and eye size (e.g., eye diameter) can be used to infer the relative importance of vision to an organism. The high metabolic cost of visual system development and maintenance suggests that large relative eye size (as it relates to body length) may have a significant ecological or evolutionary role. Elasmobranchs are morphologically diverse and inhabit a wide range of marine and freshwater niches. As energetic and ecological demands shift over time, several species occupy different predatory niches across their lifetime, yielding a large array of visual habitats. Additionally, eye size changes with body length ontogenetically, thus elasmobranchs represent an ideal group for examining scaling relationships (i.e., eye growth rate and eye size at a given body length) with respect to specific ecological lifestyle traits. Here we quantified the relationship of eye size and body length in 16 shark species and compared this scaling across species that differ in ecological lifestyle (i.e., activity level, habitat, and maximum size). Relative eye size at a given size varied across species and habitat, but not activity level or maximum size. Deep-sea species had the largest relative eye size, followed by oceanic then coastal species. In contrast, the rate at which eye size scaled with body length was the same across 13 of the 16 species and did not differ with ecological lifestyle trait. These results suggest that ecology may influence relative eye size and not the rate at which eye size scales with body length. As habitat had the greatest influence on relative eye size, future investigations should focus on ecological lifestyle traits involving visual habitat characteristics such as light level, turbidity, and migratory patterns.
