Meeting Abstract
The natural world is rich with a variety of terrestrial substrates exhibiting complex behavior. For example, granular media (GM) solidifies and fluidizes during a single step making effective movement across its surface a significant challenge. Little is known about running performance and kinematic strategies used to navigate GM, especially at different inclines. Lizards are an excellent system to study because they are found in the desert moving across level sand and inclined dunes. We hypothesized that sand specialists would run faster than generalists when running on level GM, and would show less of a performance decrement when running on inclined GM. We ran sand and fluid specialists (zebra-tailed, Callisaurus draconoides; basilisk, Basiliscus vittatus) and a generalist (Eastern collared lizard, Crotaphytus collaris) across level and incline (31.5°: angle of repose) GM on a fluidizable bed trackway. We explored differences in running speed and determined how these are modulated via basic kinematic strategies. Lizards were filmed at 500 fps (Photron SA-3), and videos were analyzed in MATLAB. All three species increased stride frequency and shortened their strides when running on the incline. However, running performance differed by species. On the level, sand and fluid specialists ran faster than generalists (F = 13.1, p<0.001). On the incline, generalists (F = 7.05, p = 0.01) and fluid specialists (F = 33.8, p<0.001) ran slower, whereas desert specialists were unaffected (F = 0.72, p = 0.39). These differences suggest that while sand specialists can overcome foot slippage during material fluidization on the incline, fluid specialists and generalists cannot. This may be due to morphological specialization and/or kinematic adjustments, which require further exploration.
