How Gait Influences Obstacle Negotiation in Lizards: Is Bipedal Better?

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Bipedal locomotion is common in many species of lizard, especially those that live in open habitats such as deserts. However, the advantages of this gait are still unclear. We hypothesize that a bipedal gait is advantageous to lizards while negotiating obstacles in the environment because of the increased field of view and/or because the anterior part of the body is elevated over the obstacle at footfall. Detailed limb kinematics and performance of bipedal running have been characterized in lizards, but our study is the first to examine the effects of obstacles in the running path, which is ecologically relevant for many species. Understanding the interactions between locomotion and ecology will help determine whether a behavior is in fact adaptive. We obtained high-speed video (500 Hz) of six-lined racerunners (Aspidoscelis sexlineata) running on a 3 m track both with and without an obstacle (2cm high and 5cm deep) spanning the width of the track. We obtained both a lateral and dorsal view in order to quantify the three-dimensional limb movements. The obstacle caused a decrease in locomotor speed for lizards employing a quadrupedal gait, but did not influence those using a bipedal gait. Whereas quadrupedal lizards often appeared to slide across the top surface of the obstacle on their bellies, bipedal lizards either maintained their gait or transitioned to a quadrupedal gait after traversing the obstacle. These data suggest that bipedal lizards are better able to remain dynamically stable when traversing obstacles, which is likely advantageous under natural conditions. Further 3-D analyses will provide more detailed kinematic data to elucidate the mechanisms underlying these performance differences.


Society for Integrative and Comparative Biology Annual Meeting (SICB)


Salt Lake City, UT