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An Integrative Analysis of Gecko Foot Morphology in Relation to the Evolution of the Adhesive System

Creative Commons 'BY-NC' version 4.0 license

The foot is a crucial component to locomotion and is greatly affected by the evolution of new functions. This dissertation examines both functional and morphological aspects of how the evolution of the dry adhesive system is associated with the evolution gecko feet.

In Chapter 1, I obtained obtained 3D movements (with high-speed video) of geckos (Phelsuma madagascariensis) running on a range of ecologically relevant inclines to examine in detail, how geckos modulate their feet with the dry adhesive system. We focused on measuring instantaneous within-foot symmetry and foot alignment relative to the body. On smaller perch diameters, geckos inverted their foot alignment and the hind foot had greater individual digit modulation than the forefoot.

Chapter 2 used a comparative phylogenetic framework to examine how digit morphology and within-foot symmetry changed with the evolution of the adhesive system. I applied geometric morphometric methods to X-rays obtained of both padbearing and padless geckos. Our results confirm that padbearing lineages tend to have shorter digits, greater within-foot symmetry and larger interdigital angles than padless lineages and this suggests repeated shifts to a similar pad-bearing morphology.

In Chapter 3, I obtained microCT scans of padbearing and padless lineages to examine how the evolution of the adhesive system is associated with shape change in the bones (astragalocalcaneum and the fourth distal tarsal) involved in the mesotarsal joint. Our results show that padbearing lineages likely have greater degrees of freedom at the mesotarsal joint as a result of having broader surfaces on the astragalocalcaneum and fourth distal tarsal.

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