Clinging ability is related to particular aspects of foot morphology in salamanders

Abstract

The interaction between morphology, performance, and ecology has long been studied in order to explain variation in the natural world. Within arboreal salamanders, diversification in foot morphology and microhabitat use are thought to be linked by the impact of foot size and shape on clinging and climbing performance, resulting in an ability to access new habitats. We examine whether various foot shape metrics correlate with stationary cling performance and microhabitat to explicitly quantify this performance gradient across 14 species of salamander, including both arboreal and nonarboreal species. Clinging performance did not correlate with foot shape, as quantified by landmark-based geometric morphometrics, nor with microhabitat use. Mass-corrected foot centroid size and foot contact area, on the other hand, correlated positively with clinging performance on a smooth substrate. Interestingly, these foot variables correlated negatively with clinging performance on rough substrates, suggesting the use of multiple clinging mechanisms dependent upon the texture of the surface. These findings demonstrate that centroid size and foot contact area are more functionally relevant for clinging in salamanders than foot shape, suggesting that foot shape need not converge in order to achieve convergent performance. More broadly, our results provide an example of how the quantification of the performance gradient can provide the appropriate lens through which to understand the macroevolution of morphology and ecology.

Keywords: arboreality; clinging; performance; salamander; shape.

FIGURE 1

a. Phylomorphospace of foot shape characterized using geometric morphometrics. The size of the points corresponds to max cling angle. Warp grids represent the shape averages of select specimens (magnitude = 1). b. Max cling angle on a smooth surface across mean centroid size corrected for mass. c. Max cling angle on a smooth surface across foot contact area corrected for mass (FCA)