Evolutionary origins of the gekkotan adhesive system

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Organismic evolution is an interactive process driven by the environment, with organisms adjusting to imposed change. The task of the evolutionary biologist is to document how, and in what ways, the environment challenges the organism to adapt. One example of an intimate and tractable relationship between organisms and environment is evident in the contact between feet and the substrate in animal locomotion. Such an interaction can be explored at various levels, from the macro to the nano scale. Gekkotan lizards (commonly collectively referred to as geckos) are well known for their highly developed adhesive system that permits them to scale surfaces such as glass with seeming ease. The extreme strength of the bond, its ability to attach and detach repeatedly without wear or loss of capability, and its ease of engagement and disengagement, are critical factors that require deeper understanding. Breakthroughs in investigative techniques have enabled us to obtain a better understanding of how these adhesive capabilities operate, and have led to broad-scale attempts to mimic these interactions synthetically, for applications that might benefit human exploitation. Geckos are a diverse group, consisting of over 1000 species, about half of which either lack or possess only a very rudimentary adhesive system. These "non adhesive" species provide avenues to investigate how the highly complex adhesive system of geckos arose, and under what environmental circumstances it was selected for. Investigation of the evolution of such a phenomenon is useful because it both permits a direct appraisal of interaction between the organism and its environment (where the "rubber hits the road"), and will provides insights into how best to mimic the system. Gekkos have elaborated their adhesive system on several (as many as 10) occasions beginning at least 54 million years ago. The degree of similarity of design in these various lineages allows assessment of what is necessary and sufficient for the operation of such a system. The thrust of this research program explores the fundamental plan of the system and investigates how we can mimic its structural and functional properties.