University of California, Berkeley
Many animals spend their lives on fine wind-blown sand. Given this, it is surprising that so little is known about the elements of an animal's body form that may aid in locomotion over sand. Much like snowshoes aid humans moving on snow, previous investigations have suggested that lizards that possess toe fringes (sideways projecting elongate scales) are adapted to running on sand, but this hypothesis has yet to be rigorously tested. In this study, the investigators will study the rapid running of three closely related sand dwelling lizards: the Mojave fringe-toed lizard (Uma scorparia), and non-fringed California (Callisaurus draconoides draconoides) and fringed Mexican (Callisaurus draconoides crinitis) subpopulations of the zebra-tailed lizard. Two general questions will be addressed in this work: 1. do fringes on the toes of lizards help them run on sand? and 2. how does variation in foot shape affect the transmission of forces from the animal to the sandy substrate? This work approaches these questions by synthesizing the fields of organismal biology, evolutionary biology, mechanical engineering, and granular physics. The researchers will use video cameras capable of recording 1000 images per second (standard cameras record at 30 images per second) to slow down the movement of animals in their natural environments as they run on a number of different substrates. Information gathered will be used to construct a robotic appendage to which models representing the diversity of foot shapes found in many different species of lizards will be attached. By "playing back" the movement patterns recorded in the field on the robotically controlled feet, the investigators will be able to measure the forces generated by different foot shapes through substrates where the lizards live. From these studies, the effect of changes in foot shape in propelling the animals forward can be directly measured. This work is one of the first to investigate how animals run on different substrates, and whether there are particular foot shapes that may be more effective for rapid movements on sand.
