Abstract
Sharks and rays are highly sensitive to chemical stimuli in their natural environment but several hypotheses predict that hammerhead sharks, with their expanded head and enlarged olfactory epithelium, have particularly acute olfactory systems. We used the electro-olfactogram (EOG) technique to compare the relative response of the scalloped hammerhead shark (Sphyrna lewini) olfactory epithelium to 20 proteinogenic amino acids and determine the sensitivity for 6 amino acids. At micromolar concentrations, cysteine evoked the greatest EOG response which was approximately twice as large as that of alanine. The weakest response was obtained for proline followed by aspartic acid and isoleucine. The olfactory epithelium showed adaptation to sequential stimulation, and recovery was related to the inter-stimulus time period. Estimated EOG response thresholds were in the sub-nanomolar range for both alanine (9.2 × 10−11 M) and cysteine (8.4 × 10−10 M) and in the micromolar range for proline and serine. These thresholds from 10−10 to 10−6 M for the scalloped hammerhead shark are comparable or lower than those reported for other teleost and elasmobranch species. Future work should focus on binary and more complex compounds to test for competition and cross-adaptation for different classes of peripheral receptors, and their responses to molecules found in biologically relevant stimuli.
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Acknowledgments
We thank T. Meredith, A. Rivera, J. Sewell and L. Sharkey for assistance with the experiments; L. Riley for sharing temporary holding tank space; and the anonymous reviewers for their comments on drafts of the manuscript. All collection methods and experimental protocols used in this study were approved by the University of Hawaii IACUC. This work was funded by Defense Advanced Research Program Agency (DARPA) to TCT and the McDowell Foundation to APS. This is contribution number 1353 from the Hawaii Institute of Marine Biology.
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Tricas, T.C., Kajiura, S.M. & Summers, A.P. Response of the hammerhead shark olfactory epithelium to amino acid stimuli. J Comp Physiol A 195, 947–954 (2009). https://doi.org/10.1007/s00359-009-0470-3
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DOI: https://doi.org/10.1007/s00359-009-0470-3