Internal vertebral morphology of bony fishes matches the mechanical demands of different environments
Baxter, Dana L.
2021
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Bony fishes reside in different habitats. Such habitats can be classified broadly into the pelagic, demersal, and benthic habitats. Pelagic fishes mainly swim in open water, benthic fishes spend most of their time on the floor of the body of water, and demersal fishes stay close to but do not rest for long times on the floor of the body of water. These different habitat categories also likely ... read morenecessitate distinct swimming styles. Pelagic fishes often swim continuously, benthic fishes often remain mostly stationary with occasional bursts of acceleration, and demersal fishes swim up and down in the water column. These swimming styles probably depend on the mechanical properties of the vertebrae and notochord. Bony fishes have hourglass shaped vertebrae, called amphicoelous vertebrae, which contain a hole, or foramen, through which the notochord (an important developmental structure) is threaded. Therefore, we hypothesize that the morphology of the vertebrae and notochord will be different to support the swimming styles that are required in the habitat in which a species resides. We predict that pelagic fishes will have narrower notochordal foramina and shallower vertebral cones because this will leave less space for flexible notochordal material, meaning that the vertebral columns of pelagic fishes will be stiffer and thus more conducive to the open water swimming required for pelagic fishes. We examined differences in vertebral morphology in 55 species from the three habitat categories by measuring vertebrae along the length of the body of each fish based on micro-computed tomography scans. From these scans, six vertebral features were measured: notochordal foramen diameter, centrum body length, and the cone angles and diameters for the anterior and posterior vertebral cones. Using a phylogenetic generalized least squares (PGLS) analysis to control for phylogeny, we found that notochordal foramen diameter, anterior cone angle, and posterior cone angle differed significantly among species from benthic, demersal, and pelagic habitats. Benthic species had significantly larger posterior cone angles than the other habitat groups, while pelagic species had significantly smaller posterior cone angles than the other habitat groups and significantly smaller notochordal foramen diameters than demersal species. We also ran a linear discriminant analysis (LDA), which showed distinct groupings for morphologies from the benthic and pelagic categories. Overall, we found significant differences in internal vertebral morphology between species in different habitat categories, differences which could accurately discriminate benthic and pelagic based on vertebrae. This might help us infer habitat differences for species where behavior and habitat may be difficult to monitor, and for fossil fishes as well. If vertebral measurements can be used to understand differences between species in multiple habitats, this work provides a window into exploring the potential habitats in which extinct species resided.
Advisor: Dr. Eric Tytellread less - ID:
- d217r399p
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