Comparative Analysis of the Flexural Stiffness of Pinniped Vibrissae

Vibrissae are important components of the mammalian tactile sensory system and are used to detect vibrotactile stimuli in the environment. Pinnipeds have the largest and most highly innervated vibrissae among mammals, and the hair shafts function as a biomechanical filter spanning the environmental stimuli and the neural mechanoreceptors deep in the follicle-sinus complex. Therefore, the material properties of these structures are critical in transferring vibrotactile information to the peripheral nervous system. Vibrissae were tested as cantilever beams and their flexural stiffness (EI) was measured to test the hypotheses that the shape of beaded vibrissae reduces EI and that vibrissae are anisotropic. EI was measured at two locations on each vibrissa, 25% and 50% of the overall length, and at two orientations to the point force. EI differed in orientations that were normal to each other, indicating a functional anisotropy. Since vibrissae taper from base to tip, the second moment of area (I) was lower at 50% than 25% of total length. The anterior orientation exhibited greater EI values at both locations compared to the dorsal orientation for all species. Smooth vibrissae were generally stiffer than beaded vibrissae. The profiles of beaded vibrissae are known to decrease the amplitude of vibrations when protruded into a flow field. The lower EI values of beaded vibrissae, along with the reduced vibrations, may function to enhance the sensitivity of mechanoreceptors to detection of small changes in flow from swimming prey by increasing the signal to noise ratio. This study builds upon previous morphological and hydrodynamic analyses of vibrissae and is the first comparative study of the mechanical properties of pinniped vibrissae.The open access fee for this work was funded through the Texas A&M University Open Access to Knowledge (OAK) Fund

Photographs of vibrissae prepared for testing.

<p>A) a California sea lion vibrissa potted in epoxy mold, B) a harp seal vibrissa potted in epoxy mold, and C) the MTS Insight apparatus testing set up with a Weddell seal vibrissa potted in epoxy mold and held horizontally for cantilever bending. The major axis of each vibrisse is facing the reader and the minor axis is perpendicular to the page.</p

Results of materials testing in four orientations.

<p>A subset of pinniped vibrissae was tested in all four orientations. D = Dorsal, A = Anterior, V = Ventral, P = Posterior. Dorsal and ventral did not differ from each other but had significantly lower mean flexural stiffness values than anterior and posterior, which also did not differ from each other. Different letters indicate significant differences between orientations.</p

Diagram of vibrissal orientation in water flow and testing orientations.

<p>Diagram of vibrissal orientation in water flow and testing orientations.</p

Results of materials testing in four orientations.

<p>A subset of pinniped vibrissae was tested in all four orientations. D = Dorsal, A = Anterior, V = Ventral, P = Posterior. Dorsal and ventral did not differ from each other but had significantly lower mean flexural stiffness values than anterior and posterior, which also did not differ from each other. Different letters indicate significant differences between orientations.</p

DS2_JVDI_10.1177_1040638718767943 – Supplemental material for Improvements in <i>Tritrichomonas foetus</i> molecular testing

<p>Supplemental material, DS2_JVDI_10.1177_1040638718767943 for Improvements in <i>Tritrichomonas foetus</i> molecular testing by Carly C. Ginter Summarell, Thomas B. Hairgrove, Megan E. Schroeder, Robert Conley, Mangkey A. Bounpheng in Journal of Veterinary Diagnostic Investigation</p

DS1_JVDI_10.1177_1040638718767943 – Supplemental material for Improvements in <i>Tritrichomonas foetus</i> molecular testing

<p>Supplemental material, DS1_JVDI_10.1177_1040638718767943 for Improvements in <i>Tritrichomonas foetus</i> molecular testing by Carly C. Ginter Summarell, Thomas B. Hairgrove, Megan E. Schroeder, Robert Conley, Mangkey A. Bounpheng in Journal of Veterinary Diagnostic Investigation</p

DS2_JVDI_10.1177_1040638718767943 – Supplemental material for Improvements in <i>Tritrichomonas foetus</i> molecular testing

<p>Supplemental material, DS2_JVDI_10.1177_1040638718767943 for Improvements in <i>Tritrichomonas foetus</i> molecular testing by Carly C. Ginter Summarell, Thomas B. Hairgrove, Megan E. Schroeder, Robert Conley, Mangkey A. Bounpheng in Journal of Veterinary Diagnostic Investigation</p