RUSSELL, A.P.: Scaling the spandrels of San Marco: Integrative functional morphology of the gekkotan adhesive system.

Attempts to explain how seta-based adhesion in geckos is brought about span the past 120 years. Recent investigations have further elucidated our understanding of this by recording the adhesive properties of single, detached setae and documenting the effect that angular orientation of the seta to the surface, and preloading of the seta have on making (and breaking) the bond. To obtain a fuller understanding of the functioning of the gekkonid adhesive system, however, an understanding of the integrative morphology and associated behavioral attributes of the entire pedal complex is necessary. Comparative studies reveal that seta-based adhesive systems have arisen on multiple occasions within the Gekkota, and also convergently in anoline iguanoids and (at least incipiently) in some scincids. Investigations of morphological variability among gekkotan pedal adhesive systems, and a comparison with those of anolines reveals the fundamental integrative design of the adhesive system and the variations upon this theme that are the legacy of different phylogenetic lineages. Morphological and behavioral correlates of digital hyperextension and their exaptation from more primitive modes of locomotion; the exaptation of derived pedal geometry and configuration; the modification of sensory feedback mechanisms; exaptation of plantar dermal tissue for scansorial control purposes; and the expression of compliance mechanisms have coalesced in various lineages in slightly different configurations and result in effective deployment and release of the setae. Analysis of pedal structure in an integrative fashion assists in understanding how the squamate seta-based adhesive system may have arisen and how it operates.