Figure 1.
Undulated and smooth vibrissal surface structures.
Surface structure of (A) a smooth vibrissa (California sea lion) and (B) an undulated vibrissa (harbor seal).
Figure 2.
Diagram of a vibrissal sample mounted in the test section of the water flume.
Schematic (figure not drawn to scale) of the recording area of the flume. The vibrissa was mounted on the sting apparatus in the center of the water column. The laser vibrometer (not pictured) was focused on the vibrissal shaft from outside the test enclosure, with the beam passing through the water column, perpendicular to the flow.
Figure 3.
Vibrational signal with distance up the vibrissal shaft.
Comparison of three example laser vibrometer recordings taken at different points along the shaft of a single vibrissal sample. Recordings were taken at 25% (top row), 50% (middle row), and 75% (bottom row) up the length of the whisker shaft and are shown as FFTs (left) and waveforms (right). The 50% recording position was determined to be optimal for signal quality and all subsequent data were recorded at this position.
Figure 4.
Vibrissal orientation for laser vibrometer recordings.
(A) Smooth (California sea lion) vibrissa at the 0° orientation. Thin edge of the vibrissa faces into the flow. (B) The same vibrissa at the 90° orientation. Broad edge of the vibrissa faces into the flow. (C) Undulated vibrissa (elephant seal) at the 0° orientation. Thin edge of the vibrissa faces into the flow. (D) The same vibrissa at the 90° orientation. Broad edge of the vibrissa faces into the flow. In these images, the direction of flow is into the page. Total length of the vibrissa in A and B is 8.1 cm, total length of the vibrissa in C and D is 9.2 cm.
Figure 5.
Position of the vibrissal array during active swimming.
(A) California sea lion with the vibrissal array protracted. In this position the vibrissae are curved ventrally. (B) Harbor seal with the vibrissal array protracted. In this position the vibrissae are curved caudally.
Figure 6.
Vibrational signal recorded from the sting mount.
Vibration of the sting apparatus, shown as a waveform (top) and FFT (bottom). The peak frequency of the vibration of the sting apparatus was consistently at 15 Hz and did not overlap with the frequency range of the signal from the vibrissae. Note that the scale used here to view the sting vibration is approximately 50 times smaller than the scales used for the vibrissae vibrations in Figures 3 and 7.
Figure 7.
Effect of angle of orientation on vibrational signal.
Comparison of FFTs at 0°, 45°, and 90° for one individual (A) California sea lion, (B) elephant seal and (C) harbor seal. In all vibrissae, peak velocity was minimal at the 0° orientation and increased as the vibrissa was rotated to 45° and then 90°.
Figure 8.
Effect of angle of orientation on mean peak frequency and velocity of vibration.
(A) Mean peak frequency across species at three angles of orientation. For all whisker types, peak frequency was highest at the 0° orientation and decreased as the vibrissa was rotated to 45° and then 90°. (B) Mean peak velocity across species at three angles of orientation. In all vibrissae, peak velocity was lowest at the 0° orientation and increased as the vibrissa was rotated to 45° and then 90°. Both graphs show pooled data for each species with +/− SE.
Table 1.
Measured and theoretical vibration frequency values pooled across subjects for each species group.
Table 2.
Measured vibration velocity values pooled across subjects for each species group.
Table 3.
ANOVA table for vibration frequency.
Table 4.
Tukey post-hoc analysis of the effect of angle of orientation on vibration frequency, within each species.
Table 5.
ANOVA table for vibration velocity.
Table 6.
Tukey post-hoc analysis of the effect of angle of orientation on vibration velocity, within each species.
Figure 9.
Comparative digital cross-sections from CT data.
Reconstructions of vibrissae from CT scan data. (A) California sea lion; (B) elephant seal; (C) harbor seal. Enlarged digital cross-sections are shown at six points along the whisker length. Scale bar represents scaling for whole whisker image. Cross-sections are approximately 4–5x enlarged. In smooth vibrissae, the cross-sectional shape is consistent between neighboring points along the shaft, while undulated vibrissae vary in cross-sectional shape between troughs to crests. The cross-sections of all vibrissae show increased flattening toward the tip.
Figure 10.
Cross-sectional area and maximum caliper width of vibrissal cross-sectional profiles from CT data.
Calculated cross-sectional area along the vibrissal length for three subjects of each species. (A and D) California sea lion; (B and E) elephant seal; (C and F) harbor seal. In all vibrissae, the cross-sectional area gradually decreased from the base of the shaft towards the tip. In undulated vibrissae, the cross-sectional area remained relatively consistent between the crests and troughs, while the maximum caliper width increased and decreased with each undulation.
Figure 11.
Eccentricity of vibrissal cross-sectional profiles from CT data.
Measure of eccentricity, or ellipticity, along the vibrissal length for three subjects of each species. (A) California sea lion; (B) elephant seal; (C) harbor seal. The eccentricity of a perfect circle is 0, while the eccentricity of an ellipse would be >0 but <1. Overall, both smooth and undulated vibrissae show similar degrees of eccentricity. In smooth vibrissae, eccentricity is consistent between neighboring points along the shaft, while in undulated vibrissae eccentricity oscillates with each trough and crest.
Figure 12.
Theta of vibrissal cross-sectional profiles from CT data.
Angle of the major axis of the cross-section from horizontal. (A) California sea lion; (B) elephant seal; (C) harbor seal. For smooth vibrissae, theta measurements deviate from zero, while in undulated vibrissae theta measurements centered around zero across the entire length of the vibrissa.