Meeting Abstract

P2-116    Surface Roughness of the Polar Bear Paw Pad and its Relevance to Traction on Snow Orndorf, N; Garner, AM*; Dhinojwala, A; The University of Akron, Akron, OH USA; The University of Akron, Akron, OH USA; The University of Akron, Akron, OH USA nao15@uakron.edu http://H2Orndorf.com/research

Mammalian paw pads are thought to enhance friction during locomotion, yet the respective structure-function relationship is largely understudied. Specifically, the surface roughness on the paw pads has the potential to greatly influence friction but has received little attention. Bears vary considerably in their habitat and substrate use, providing an opportunity to examine variation in pad surface roughness in a comparative morphological framework and make functional predictions. Papillae on polar bear paw pads have repeatedly been considered adaptations for frictional enhancement on ice and snow, yet this assertion is based on a single morphological study that only examined the paw pad of the polar bear. Considering that no comparisons were made with other species of bear that exploit different habitats and substrates, it is unclear if their presence or structure is related to substrate use. Here, we quantify the surface roughness of the paw pads of four species of bear over 5 orders of magnitude by calculating the surface roughness power spectral density in order to predict their relative friction performance on snow. We find that the interspecific variation in papillae base diameter can be explained by paw pad size, but that papillae height is 1.5 times larger on polar bear paw pads than the other species. While the forepaw pad of the polar bear is 1.7 times smaller than that of the other species, the roughness on their pads creates 1.3 times as much true contact area with snow than its closest extant relatives. Roughness at length scales that do not contribute to friction on snow (i.e., those smaller than 6 ?m) has a lower amplitude on polar bears compared to the other species. These results suggest that the surface roughness of polar bear paw pads improves frictional performance on snow compared to its closest relatives, supporting the hypothesis that polar bear paw pads are adapted for better traction in their snowy environment.