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Adhesive pads in anurans: Their origin, shape, and performance

Aldridge, Mitchell
Unveiling the origins of morphological diversity in functional traits can be difficult, particularly when diverse structures purportedly have the same function. Doing so thus requires a focus on how performance maps onto morphology. Here, I addressed several topics regarding the evolution of adhesive pads in frogs. First, I estimated the number of times adhesive pads independently originated in anurans, using pad presence-absence data from 1297 species and multiple methods to determine the upper and lower bounds of independent origins. I found that adhesive pads most likely evolved once at the base of Neobatrachia, a major clade containing 95% of all anuran species. Moreover, I found that adhesive pads have been lost and regained multiple times. Next, I characterized pad shape for 785 species, then tested for a correlation between adhesive-pad shape and the underlying bone structure, namely whether the terminal phalanges are mediolaterally expanded, using a subset of 292 species. I then used model fitting to address the order of evolution for adhesive-pad shape and its underlying bone structure. Adhesive-pad shape correlated with the underlying bone structure, though the order in which these morphologies evolved was unclear. Finally, I collected adhesive performance data for seven species to test for differences in adhesive performance across pad shapes. There were no differences in performance for one shape metric, though the other correlated with adhesive performance on some substrates and not others. Overall, my thesis provides insight into how morphological diversity develops and the consequences of that diversity in a relatively poorly understood system.