Left in the dust: differential effectiveness of the two alternative adhesive pad configurations in geckos (Reptilia: Gekkota)

摘要

Two distinctive patterns of adhesive toepad are found in the Gekkota - terminal leaf-like pads situated at the distal ends of the digits, and basal pads that encroach more proximally along the digits, are proportionally larger and are associated with more than just the ungual and distal portion of the penultimate phalanges. Although these two configurations have long been recognized, there has been no explanation of whether or not they are functionally different. A small offshore island provided a potential arena for testing the possibility of differential functionality of these two patterns. Euleptes europaea, a leaf-padded taxon, is widespread on Giraglia Island (Corsica), whereas Tarentola mauritanica, a basally padded recent colonizer, has remained restricted to its one concrete building. Challenges to adhesion occur on dusty surfaces, and the self-cleaning mechanism of gecko setal fields can be rendered ineffective if the dust is ubiquitous. Giraglia is composed of prasinite, an inherently friable and dusty schist. The leaf-like terminal pads of E.europaea can be withdrawn from close contact with dusty surfaces, leaving the claws alone to provide traction. The digits of T.mauritanica more fully integrate the claws and adhesive pad, with full-digit hyperextension rendering the claws alone incapable of gripping the surface. Colonization of Giraglia by T.mauritanica has failed because its adhesive system is incompatible with the island's rocky terrain. This has permitted the relictual E.europaea to persist in the face of potentially intense competition. Our findings shed light on the previously noted association of leaf-like pads with rupicolous habits, and indicate that an enhanced understanding of particular surfaces that leaf-padded geckos exploit may further clarify how definitive these associations are.