KORFF, W.L.: Slip slidin’ away: Comparative kinematics of two sand dwelling lizard species

Convergence of morphological characters in similar environments is often cited as an indicator of morphological adaptation. Comparative studies that are designed to elucidate relationships between morphology and performance can strengthen conclusions of adaptive convergence that are based solely on correlation. Lizards with fringed toes provide an opportunity to assess the form/function relationship in an adaptive context. Toe fringes have evolved independently 26 times in seven families of lizards. Presence of fringes has been correlated with sandy habitats, but the functional consequence of fringes has yet to be rigorously tested. To test whether fringes convey a performance advantage, I compared the locomotion of two closely related sand dwelling lizards, the zebra-tailed lizard (Callisaurus draconoides) and the Mojave fringe-toed lizard (Uma scorparia). While both species co-occur in the same habitat, Uma have fringes while Callisaurus do not. In the field I utilized high-speed video (250fps) to quantify the amount of “slippage” in the sand for both species. Animals were brought back to the lab where I used two orthogonal high-speed cameras (1000fps) to capture the 3-D movement of the hindlimb as it interacted with the sandy substrate. No difference is apparent between the fringe-toed species and the non fringe-toed species in foot slippage, suggesting that there may be alternative strategies to contend with sandy substrates.