Are they arboreal? Climbing abilities and mechanics in the red-backed salamander (Plethodon cinereus).

While red-backed salamanders (Plethodon cinereus) are most often observed in terrestrial forested areas, several studies report arboreal substrate use and climbing behavior. However, salamanders do not have any of the anatomical features commonly observed in specialized climbing species (e.g., claws, setae, suction cups). Instead, salamanders cling to surfaces using the shear and adhesive properties of their mucous layer. In this study, we explore the capabilities and spatiotemporal gait patterns of arboreal locomotion in the red-backed salamander as they move across twelve substrate conditions ranging in diameter, orientation, and roughness. On arboreal substrates, red-backed salamanders decreased locomotor speed, stride frequency, phase and stride length, and increased duty factor and stride duration. Such responses have been observed in other non-salamander species and are posited to increase arboreal stability. Furthermore, these findings indicate that amphibian locomotion, or at least the locomotor behavior of the red-backed salamander, is not stereotyped and that some locomotor plasticity is possible in response to the demands of the external environment. However, red-backed salamanders were unable to locomote on any small-diameter or vertically-oriented coarse substrates. This finding provides strong evidence that the climbing abilities of red-backed salamanders are attributable solely to mucous adhesion and that this species is unable to produce the necessary external "gripping" forces to achieve fine-branch arboreal locomotion or scale substrates where adhesion is not possible. The red-backed salamander provides an ideal model for arboreal locomotor performance of anatomically-unspecialized amphibians and offers insight into transitionary stages in the evolution of arborealism in this lineage.