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 non-arboreal 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.

Included is an R script used for all analyses, a tps file including the foot shape data as quantified by 2d geometric morphometrics, a csv with cling data, and a phy file which is a phylogeny from Bonett and Blair 2017, pruned to match the species used in this study.

See Baken and O'Donnell 2021 for methodological details.

Baken, E. K., and M. K. O'Donnell. 2021. 

Bonett, R., and A. Blair. 2017. Evidence for complex life cycle constraints on salamander body form diversification. Proceedings of the National Academy of Sciences 114(37):9936-9941.