Term of Award

Summer 2020

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Department of Biology

Committee Chair

Christine Bedore

Committee Member 1

Stephen Vivies

Committee Member 2

Lance McBrayer

Abstract

Adaptations of visual systems, such as acuity, sensitivity, and eye size 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 allometrically, 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 I quantified the relationship of eye size and body length in 19 shark species and, after accounting for phylogeny, compared this scaling across species that differ in ecological traits (i.e., activity level, habitat type, habitat complexity, and diet). Relative eye size at a given size varied across species and habitat type, but not activity level, habitat complexity, or diet, all of which had a strong phylogenetic signal (λ = >0.9). Deep-sea species had the largest relative eye size, followed by oceanic and coastal species which did not differ from each other. In contrast, the rate at which eye size scaled with body length was the same across all species and did not differ with ecological lifestyle trait. These results suggest that habitat type may influence relative eye size and not the rate at which eye size scales with body length. As habitat type 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.

Research Data and Supplementary Material

No

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