First published online October 7, 2008
Journal of Experimental Biology 211, 3205-3213 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.012468
Ontogenetic changes in the structural stiffness of the tailstock of bottlenose dolphins (Tursiops truncatus)
S. A. Etnier1,*,
W. A. McLellan2,
J. Blum3 and
D. A. Pabst2
1 Department of Biological Sciences, Butler University, Indianapolis, IN 46208,
USA
2 Biology and Marine Biology, University of North Carolina Wilmington,
Wilmington, NC 28403, USA
3 Mathematics and Statistics, University of North Carolina Wilmington,
Wilmington, NC 28403, USA
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Fig. 1. En utero position of a fetal dolphin (PTM 114f, total length 81
cm). The dorsal fin and tail flukes are still floppy, with the flukes
juxtaposed to the chin. Note the presence of prominent fetal folds. The scale
bar is 15.8 cm in length.
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Fig. 2. (A) Schematic drawing of the bending apparatus used for determining
structural stiffness (EI, Nm2). The thick gray line
represents the central axis of the animal and the triangle at the bottom of
the image represents the flukes. (B) Actual image of the bending apparatus as
seen from above. The specimen shown here is a Grampus griseus (WAM
570, total length 215 cm), positioned for lateral deformations. The animal is
immobilized with two ratchet tie-downs cranial and caudal to the pectoral fin.
The central axis of the animal is marked with zinc oxide dots, while the
center of the dorsal fin, the anus and the mid-peduncle are marked with
horizontal white lines.
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Fig. 3. Representative diagrams showing dorsoventral and lateral deformations of
the caudal tailstock of one individual from each of the different life-history
stages under various loads. The vertical line represents the center of the
dorsal fin and the head is pointing to the right in all images. The lines
showing deformation of the tailstock depict the central axis of the animal, as
determined by positions 2, 4, 6 and 8 as described in Materials and methods.
The direction and applied load are listed next to the resultant deformation,
while the neutral line shows the posture of the animal with no applied load.
(A) Dorsal view of lateral deformation for loads ranging from 0 to 49 N. In
the fetus, bending to the right occurred freely, with no applied load (R no
load), while maximum deformation (R max. load) occurred with the application
of a load too small to be quantified by our apparatus. (B) Lateral view of
dorsoventral deformations for loads ranging from 0 to 66.6 N. Note that the
images are not to scale. L, left; R, right; D, dorsal; V, ventral; TL, total
body length (cm).
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Fig. 4. Overall curvature (m–1) for an ontogenetic series of
dolphins when deformed with a maximal load. Values are shown for deformation
in the lateral (mean value for both left and right), dorsal and ventral
directions. The maximal load is the point at which any increased load resulted
in no further deformation or caused unnatural distortion of the body. Vertical
dotted lines distinguish different life-history stages.
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Fig. 5. Structural stiffness and stiffness constants for an ontogenetic series of
dolphins. Values are shown for deformation in the lateral (mean value for both
left and right), dorsal and ventral directions. Vertical dotted lines
distinguish different life-history stages. (A) Structural stiffness was
calculated for deformations that were less than 10% of total body length and
thus often represent single data points. For dorsal and ventral deformations,
the average standard deviation was 7.5 and 0.8, respectively. For lateral
deformations, the average standard deviation was 9.8. Fetal deformations
typically exceeded the stated criterion, even with loads that were too small
to be measured with our apparatus. For these animals, we assumed a load of
0.98 N and used the resultant deformations. Thus, these values should be
considered approximations. (B) Stiffness constant (k) for an
ontogenetic series of dolphins. Values were calculated for all deformations
that exceeded 10% of total body length.
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Fig. 6. (A) The neutral zone for an ontogenetic series of dolphins. The neutral
zone is defined as the deformation exhibited with no measurable applied load.
(B) The relative neutral zone (neutral zone/total length) for the same
specimens. Vertical dotted lines distinguish different life-history
stages.
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© The Company of Biologists Ltd 2008
