RIVERA, G.*; SAVITZKY, A.H.; HINKLEY, J.A.; Old Dominion University; Old Dominion University; NASA Langley Research Center: The integument of the Common Gartersnake (Thamnophis sirtalis): Mechanical properties and the role of skin in feeding

The evolution of advanced snakes has involved morphological restructuring associated with the ability to ingest large-bodied prey. Previous studies investigating ophidian feeding mechanics have focused on adaptations associated with increased gape. While gape represents an initial factor limiting consumption of large prey, skin compliance is an important constraint during prey transport. Skin overlying prepyloric regions of the body must be compliant to accommodate bulky prey, while postpyloric skin need not be as compliant. To test for such regional variation in mechanical properties of the skin, we excised circumferential strips of skin from 9 regions along the body axis of 11 male Common Gartersnakes (T. sirtalis), and subjected each sample to a uniaxial tensile test. Tensile tests were conducted with stress applied along the transverse axis of each sample, thereby simulating the distention of skin during feeding. The skin of T. sirtalis exhibits substantial variation in mechanical properties among regions of the body. Prepyloric skin is more compliant than postpyloric skin. Mean strain was highest in the anteriormost body region and decreased to nearly 50% of the maximum caudally. We propose that the regional variation in skin compliance along the body axis is a function of three primary morphological factors: the amount of intersquamous skin, skin thickness, and the number of dorsal scale rows. Each of these morphological factors enhances skin compliance in anterior body regions and reduces compliance in caudal body regions, consistent with the demands of macrophagy. In addition, we propose a simple model of how these three characteristics interact with body shape to allow for feeding on large-bodied prey.