Does Variation in Gecko Toe Pad and Claw Morphology Reflect Adaptive Evolution to Microhabitat?

Abstract Body : Geckos are best known for their ability to “stick” to and climb a variety of surfaces. Although much is known about the basic anatomy and mechanics of the highly adept frictional adhesive toe pads from model species, attachment morphology within this large clade of lizards (more than 1800 species) is highly diverse. For example, some geckos exhibit toe pads and digital claws, while others lack one or both of these features. Moreover, geckos are found within many habitats and use substrates that range widely in roughness and compliance (e.g., rock, vegetation, and sand). To begin to discern the functional and evolutionary significance of this diversity, a phylogenetic framework was applied to compare various aspects of pad and claw morphology from dissected preserved specimens and microhabitat use observations (collected from the literature) in 112 species. Evidence for adaptive evolution of toe pads and claws was observed from phylogenetic least-squares regressions. Species that climbed rock and/or vegetation showed larger toe pad area and inner claw curvature relative to more ground-dwelling species, and rock-climbing specialists exhibited the longest setae, the microscopic toe pad hairs that create frictional and adhesive forces with a surface. This study represents an important first step in understanding the ecological context and evolutionary trajectory that continues to shape morphological diversity in gecko attachment features.