Material properties of skin in the flying snake Chrysopelea ornata

Abstract

In snakes, the skin serves for protection, camouflage, visual signaling, locomotion, and its ability to stretch facilitates large prey ingestion. The flying snakes of the genus Chrysopelea are capable of jumping and gliding through the air, requiring additional functional demands: its skin must accommodate stretch in multiple directions during gliding and, perhaps more importantly, during high-speed, direct-impact landing. Is the skin of flying snakes specialized for gliding? Here, we characterized the material properties of the skin of Chrysopelea ornata and compared them with two nongliding species of colubrid snakes, Thamnophis sirtalis and Pantherophis guttatus, as well as with previously published values. The skin was examined using uniaxial tensile testing to measure stresses, and digital image correlation methods to determine strains, yielding metrics of strength, elastic modulus, strain energy, and extensibility. To test for loading orientation effects, specimens were tested from three orientations relative to the snake's long axis: lateral, circumferential, and ventral. Specimens were taken from two regions of the body, pre- and pos-tpyloric, to test for regional effects related to the ingestion of large prey. In comparison with T. sirtalis and P. guttatus, C. ornata exhibited higher post-pyloric and lower pre-pyloric extensibility in circumferential specimens. However, overall there were few differences in skin material properties of C. ornata compared to other species, both within and across studies, suggesting that the skin of flying snakes is not specialized for gliding locomotion. Surprisingly, circumferential specimens demonstrated lower strength and extensibility in pre-pyloric skin, suggesting less regional specialization related to large prey.

Keywords: elastic modulus; extensibility; flying snake; material properties; skin; strain energy; strength.