Salamander ecomorphology reveals a unique suite of climbing adaptations

Many salamanders climb extensively but lack morphological adaptations, such as claws or adhesive toe pads, found in other climbing tetrapods. Here, we compared climbers and non-climbers from the salamander genera Aneides and Plethodon to evaluate potential morphological adaptations for climbing across multiple levels of biological organization. We integrated body shape morphometrics, allometry of the autopods (manus and pes), mechanical advantage of the digits and comparisons of epithelial microstructures. Compared with non-climbers, climbers have longer limbs that likely facilitate faster climbing and have larger and positively allometric autopods that likely yield superior clinging performance. Longer digits increase climbing reach at the expense of grip force, but climbers circumvent this trade-off with phalangeal morphologies that increase the mechanical advantage of their digits. A few species also have pes epithelia that may increase adhesion or friction but epithelial morphology was largely uncorrelated with habitat use. While scansorial species of Aneides and Plethodon share some characteristics with other genera of climbing salamanders, our results reveal subtle differences between rock-climbing and tree-climbing salamanders that reflect distinct selective pressures imposed by their microhabitats. Many-to-one mapping enables alternate strategies to address the challenges of climbing and helps to explain the abundance and diversity of climbing tetrapods.