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First published online July 25, 2005
Journal of Experimental Biology 208, 2913-2922 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01715

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Mechanical properties of the integument of the common gartersnake, Thamnophis sirtalis (Serpentes: Colubridae)

Gabriel Rivera^1,*, Alan H. Savitzky¹ and Jeffrey A. Hinkley²

¹ Department of Biological Sciences, Old Dominion University, Norfolk, VA 23529, USA
² Advanced Materials and Processing Branch, NASA Langley Research Center, Hampton, VA 23681, USA

View larger version (58K): [in a new window]   Fig. 1. Dorsal view of Thamnophis sirtalis. Circles mark the position at which each of the nine regions (a–i) is centered and are spaced at increments of 10% of the ventral scale count. The triangle indicates the level of the cloaca and represents 100% of the snout–vent length. Scale bar, 1 cm.

View larger version (28K): [in a new window]   Fig. 2. Placement of the aluminum grips and direction of the applied load during mechanical tests. The load was applied along the long axis of the sample, which corresponds to the circumference of the body. Ventral scales are shaded.

View larger version (16K): [in a new window]   Fig. 3. Stress–strain curves for a single specimen (AHS L-9597). Curves were produced from data collected during uniaxial tensile tests. Each of the nine curves represents data collected from a single sample. Note the considerable strains attained (0.50–1.25) before appreciable stress is detected.

View larger version (11K): [in a new window]   Fig. 4. Regional variation in skin thickness among body regions. Note the gradual increase in thickness posteriorly. Symbols represent means ± S.E.M. (N=11 for regions a–h; N=10 for region i).

View larger version (8K): [in a new window]   Fig. 5. Regional variation in number of dorsal scale rows. Scale-row reduction occurs at mid-body, approximately at the level of the pylorus. Data on scale rows were collected from 108 skin samples obtained from 12 specimens. Values in parentheses indicate the number of samples included for regions in which all 12 samples were not used. Two skin samples (one each for regions e and f) in transitional states of scale-row reduction were excluded from this data set. The location of the pylorus, between regions e and f, is indicated by a broken line.

View larger version (11K): [in a new window]   Fig. 6. Regional variation in strain at a stress of 2.0 MPa. Strain decreased posteriorly at a similar rate at both stress levels (1.0 and 2.0 MPa). Symbols represent means ± S.E.M. (a, c, e, i, N=10; b, N=9; d, f–h, N=11). Results of a Tukey multiple comparison test identify homogeneous regions.

View larger version (12K): [in a new window]   Fig. 7. Regional variation in elastic modulus at a stress of 2.0 MPa. Elastic moduli increased posteriorly at a similar rate at both stress levels. A distinct increase exists between the moduli of anterior regions (a–e) and posterior regions (f–i) at both stresses, indicating a sharp increase in skin stiffness. Symbols represent means ± S.E.M. (a, c, e, i, N=10; b, N=9; d, f–h, N=11). Results of a Tukey multiple comparison test identify homogeneous regions.

View larger version (10K): [in a new window]   Fig. 8. Regional variation in body circumference at rest and at a constant stress of 2.0 MPa. Open circles represent circumference at rest; solid circles represent circumference at constant stress. Symbols represent means ± S.E.M. The location of the pylorus relative to the nine regions of the body is indicated (broken line) and was determined by dissection of two specimens.

View larger version (13K): [in a new window]   Fig. 9. Relationship between skin thickness and the strain attained at a constant stress (2.0 MPa) for each of the 93 samples for which mechanical data were collected.