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Function, Morphology, and Evolution of Gecko Locomotion: The Importance of Ecology and Substrate


Locomotion is a central tenet of life for many organisms that is inherently tied to the surrounding physical environment. Geckos represent a speciose and phenotypically diverse clade of lizards that are found within many habitats and move on a variety of substrates. Although much is now known about the integration and mechanics of the highly adept frictional adhesive toe pads from intensive laboratory study within model species, the functional and evolutionary significance of phenotypic diversity within geckos is ripe for investigation. This dissertation thus brings ecological context to the foreground to begin to address this large gap. In Chapter 1, we collected field observations and locomotor trials of surface compliance transitions in a cursorial day gecko, Rhoptropus afer, to examine how this species responds to sudden changes in substrate conditions encountered in nature. This species maintained high-speed running while altering its posture and stance time when transitioning into and out of sand collected from its habitat. In Chapter 2, we used experimental claw manipulation (i.e., partial removal) in the arboreal species, Thecadactylus rapicauda, to assess the functional interplay of adhesive toe pads and claws on natural and artificial surfaces of different roughness. After partial claw removal, static clinging performance significantly declined on non-smooth surfaces, and geckos tended to adjust their foot kinematics to increase contact duration on smooth and rough surfaces at both horizontal and low incline, although their ability to accelerate from a stationary position was not significantly altered. Finally, in Chapter 3, we took a phylogenetic comparative approach (112 gecko species) to test if morphological variation in toe pads and claws represents adaptive evolution to general habitat use. We found that species using more scansorial habitats tended to have larger, longer pads and more curved claws, with saxicolous species having longer setae than all other groups.

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