Descriptive and functional anatomy of the digital vascular system of the tokay, Gekko gecko

Abstract

The vascular system of the digits of the tokay is more complex than has hitherto been suspected and has a configuration which suggests it is intimately involved in the process of adhesion. Distinction can be made between lamellae (expanded scales beneath the proximal portion of the digit) and scansors (elaborations of lamellae that contain a large amount of subdermal material and therefore do not technically qualify as scales). Such a distinction is made on anatomical grounds and can be appreciated only if anatomical investigation is carried out. There are no externally obvious features by which lamellae and scansors can be distinguished, except position. Scansors are found beneath hyperextensible phalanges, whereas lamellae are located more proximally and are not subjected to digital hyperextension during locomotion. Whether this distinction can be applied to other pad-bearing geckos and to anoline lizards remains to be seen. The large sinus beneath the penultimate phalanx appears to govern the pressure within the system; the reticular blood systems of the scansors appear to manifest the pressure changes with respect to the locomotor substratum. Changes in pressure within the system probably permit the overlapping scansors to comply precisely with each other and with the substratum. The presence of a system based on fluid pressure differentials means that scansors are deformable along multiple axes at any one time, thus permitting a high degree of compliance with their entire surroundings. It is probable that changes in pressure within the system promote release from the substratum as well as compliance with and attachment to it. The mechanism of control of the system awaits further investigation. The pattern of the digital vascular complex has been considered in relation to the mode of operation of the digits during locomotion. Distal drainage of the sinus is ideally suited to the activity of hyperextension of the digits. This combination permits sequential pressurizing and depressurizing of the scansors and allows the bond to be created or broken in a gradual fashion rather than in an all-or-none manner. By avoiding sudden shifts in the pattern of dynamic loading (the bond is not broken instantaneously but sequentially), the risk of transverse instability during locomotion is lessened. The increase of loading on the other feet is thus gradual. The importance of this is discussed more fully elsewhere in a consideration of the structure and function of scansors. That the digits of the tokay are hyperextended during horizontal as well as vertical locomotion (Russell, '75, p. 463) can now be rationalized not only from the point of view of protection of the setae but also because of the manner in which the vascular system of the digits functions and is drained.

Gecko toe and lamellar shear adhesion on macroscopic, engineered rough surfaces

“…Toe pads are in-folded to form rows that hold modified keratinized scales called lamellae. These lamellae are composed of hundreds of tiny hairs called setae, which are then further subdivided into hundreds of nanoscale-sized spatulae (Russell, 1981;Russell, 1986). These spatulae individually adhere to surfaces using intermolecular van der Waals forces (Autumn et al, 2000;Autumn et al, 2002).…”

“…Russell (Russell, 1981;Russell, 1986;Russell, 2002) proposed that the intermediate structures are used to cushion the foot against the surface, and to allow the flexible lamellae to conform more closely to the surface to which they are adhering. Another theory on the function of the intermediate structures is that the size, shape and angle of the larger hierarchical structures aid in rapid detachment of the foot (Gao et al, 2005;Cheng et al, 2012).…”

Gecko Adhesion as a Model System for Integrative Biology, Interdisciplinary Science, and Bioinspired Engineering

“…Each diamond-shaped structure is the branched end of a group of four setae clustered together in a tetrad; (e) nanoscale array of hundreds of spatular tips branching from a single gecko seta; ( f ) the terminal spatular branches are widened and flattened at the tip; and ( g) these flat faces interface with the substrate to produce strong attachment. thousand species (Han et al 2004) with adhesive toe pads, encompassing an impressive range of morphological variation at the spatula, seta, scansor, and toe levels Autumn & Peattie 2002;Maderson 1964;Irschick et al 1996;Peterson & Williams 1981;Ruibal & Ernst 1965;Russell 1975Russell , 1981Russell , 1986Schleich & Kästle 1986;Stork 1983;Williams & Peterson 1982). Setae have even evolved on the tails of some gecko species (Bauer 1998).…”

Gecko adhesion: evolutionary nanotechnology

“…Gecko setae are formed primarily of beta-keratin (Maderson 1964;Russell 1986;Alibardi 2003) with some alpha-keratin components (Rizzo et al 2006). While the tokay is currently the best studied of any adhesive gecko species, there are over a thousand species of gecko (Han et al 2004), encompassing an impressive range of morphological variation at the spatula, seta, scansor and toe levels (Maderson 1964;Ruibal & Ernst 1965;Russell 1975Russell , 1981Russell , 1986Peterson & Williams 1981;Williams & Peterson 1982;Stork 1983;Schleich & Kästle 1986;Russell & Bauer 1988, 1990aRoll 1995;Irschick et al 1996;Autumn & Peattie 2002;Arzt et al 2003). Setae have even evolved on the tails of some gecko species (Bauer 1998).…”