Meredith, Tricia L.

The functional impacts of olfactory rosette variation in elasmobranchs is unresolved. Our goal was to quantify rosette morphology and shape from 14 species using dissections, phylogenetic comparisons, and microCT imaging. We hypothesized that lamellar count and rosette shape (fineness ratio) would not scale with animal size, but internal rosette size variables must scale positively. We found that fineness ratio and lamellar counts varied significantly among species, and were positively correlated. The first two principal components of the pPCA explained 82% of the variation, with fineness ratio and lamellar count contributing the most. There were no significant differences between rosette structure or volume when comparing dissected values to in situ values obtained using diceCT. Based on our results, we hypothesize that variations in rosette shape and morphology will impact hydrodynamics and optimize odorant detection, and these data can be used to create 3D models for future hydrodynamic studies.

The olfactory system is the most highly developed system for molecular sensing in vertebrates. Despite their reputation for being particularly olfactory driven, little is known about how this sense functions in elasmobranch fishes. The goal of this dissertation was to examine the morphology and physiology of elasmobranchs to compare their olfactory system with teleost fishes and more derived vertebrates. To test the hypotheses that elasmobranchs possess greater olfactory sensitivities than teleosts and that lamellar surface area is correlated to sensitivity, I compared the surface area of the olfactory lamellae and the olfactory sensitivities of five phylogenetically diverse elasmobranch species. The olfactory thresholds reported here (10-9 to 10-6 M) were comparable to those previously reported for teleosts and did not correlate with lamellar surface area. Since aquatic species are subject to similar environmental amino acid levels, they appear to have converged upon similar amino acid sensitivities. To test the hypothesis that elasmobranchs are able to detect bile salt odorants despite lacking ciliated olfactory receptor neurons (ORNs), the type of ORN that mediates bile salt detection in the teleosts, I quantified the olfactory specificity and sensitivity of two elasmobranch species to four, teleost-produced C24 bile salts. Both species responded to all four bile salts, but demonstrated smaller relative responses and less sensitivity compared to teleosts and agnathans. This may indicate that elasmobranchs don't rely on bile salts to detect teleost prey. Also, the olfactory system of elasmobranchs contains molecular olfactory receptors for bile salts independent of those that detect amino acids, similar to teleosts.