Limb kinematics and morphology improve salamander climbing performance

Hundreds of plethodontid salamander species can climb vertical structures, despite lacking morphological adaptations typically found in other climbing tetrapods. To compensate, salamanders likely rely more on behavioral modifications to mediate the relationship between their relatively generalist morphologies and climbing performance. Here, we examined four plethodontid species (Aneides aeneus, Aneides lugubris, Aneides hardii and Plethodon glutinosus) that differ in their habitat preferences, climbing tendencies and limb morphologies. Using 3D high-speed videography, we compared how these species adjust their gait and limb kinematics while traversing a flat surface inclined at 0, 45, 80 and 90 deg. We found that all species could climb vertically (or near vertically for A. hardii) using similar gait and kinematic changes that increase stability. For instance, all species used a single-step gait, increased duty factor, reduced stride length and reduced stride frequency while their bodies were positioned closer to the substrate at the highest inclines compared with 0 or 45 deg inclines. However, highly scansorial species (A. aeneus and A. lugubris) climbed faster than the other species. The enhanced abilities of scansorial species may be attributable to their longer limbs that enable longer strides as well as their unique foot morphologies - coupled with changes in foot orientation - that facilitate better attachment through grasping. Overall, we propose that behavioral changes are sufficient for adequate climbing, but subtle morphological changes promote exceptional climbing performance. This likely explains the prevalence of climbing abilities across ecologically and morphologically diverse plethodontid salamanders.