What Cyrtodactylus Geckos Can Tell Us about the Evolution of Stickiness in Lizards – Anole Annals

Like anoles, geckos are famous for their adhesive toepads, enabling astonishing climbing abilities. Since adhesive toepads evolved independently in geckos and anoles, these two rather distantly related lizard clades have become the poster-children of convergent evolution in climbing. But, astonishingly, how such a complex system actually evolves has until recently garnered little attention. And while anoles have long been celebrated for their sticky pads, the literature tends to treat the spectacular adhesive system in a binary fashion as either being present (full pads) or absent (pad‑less) in geckos– despite the fact that earlier research already indicated that this might not be the case.

The genus Cyrtodactylus (~ 400 species) is an excellent vehicle for studying the transition from a pad‑less ancestor to a fully adhesive foot because its members occupy a dizzying array of habitats — from ground‑dwelling leaf‑litter specialists to tree‑crown acrobats — quite comparable to Anolis lizards in this regard. And not only that, but our previous work has revealed that Cyrtodactylus displays a continuum of sub‑digital scale shapes ranging from tiny round scales to broadened, lamella‑like “incipient toepads” (Riedel et al. 2024).

So, building on these previous studies, we embarked on a project to look at the sub-digital microstructures of Cyrtodactylus geckos as the logical next step. The dry‑adhesive systems of geckos and anoles rely on arrays of microscopic filaments called setae (Fig. 2). In geckos four filament types have been described (Garner & Russell 2021): spinules, spines, prongs, and setae (Fig. 2). While spines ancestrally cover most parts of the skin of geckos and anoles alike, and likely evolved for self-cleaning purposes (lotus effect), spines and prongs have been hypothesized to be “pre‑adhesive” adaptations that improve traction on rough surfaces. Only setae have been proven to generate sufficient van‑der‑Waals forces capable of generating adhesive forces of sufficient magnitude to support the entire animal.

Figure 2: Microstructures found in geckos and anoles. Spinules are short, tapered filaments covering the majority of the skin of geckos and anoles alike. Spines are somewhat longer with pointier tips, while prongs have blunt, flattened tips. Setae are long filaments possessing triangular tips, called spatulae. Illustration from Ginal et al. 2026 (redrawn and modified from Garner & Russell 2021).

The actual study, building upon a hypothesis formulated 50 years ago (Russell, 1976), began with checking museum specimens for the presence of subdigital microstructures using light microscopy, since the outer skin layer is often lost in specimens stored in ethanol for long time periods. Of the 86 specimens examined, spanning 30 species from four museum collections, 53 specimens belonging to 27 species were suitable for examination with the scanning electron microscope (SEM), which is the standard tool for studying integumentary microstructures in reptiles. Although representing only a small fraction of the 400 species of Cyrtodactylus, this sample constituted a sufficiently broad phylogenetic coverage across the genus. It also incorporated representative stages in the sub-digital scale shape continuum and species representing multiple habitat preferences (ecotypes). SEM imaging was used to first categorize microstructures into the four known types (Fig. 2) and then to quantify various parameters, such as filament length, diameter, and density, which are known to vary across species and microstructure types, all of which are related to the function of these structures. From these measurements, effective bending stiffness – a measurement of flexibility, which is particularly important for setal function – could be calculated. We then applied different modelling approaches to test for correlations of both microstructure types and measurements with ecotypes and reconstructed their evolutionary history to compare their evolution with the evolution of scale shapes as reconstructed in our previous study.

We found that spines are likely the ancestral condition for the genus at large and that prongs evolved three times independently from spines, while setae evolved two times – once in the intertidal species C. seribuatensis and once in a large crown group including many but not all arboreal or saxicoline (rock-dwelling) lineages (Fig. 3). This indicates that microstructure types are phylogenetically constrained. Interestingly, the two arboreal clades with strongly expressed incipient toepads (lamella-like subdigital scales) are nested within the setae-bearing crown group, indicating that the evolution of setae preceded the evolution of lamella-like scales in these lineages. Thus, our results suggest that adhesive competence may arise before the classic “lamella” morphology. However, C. consobrinus (a trunk species) shows the incipient toe pad gross morphology of its subdigital scales but lacks setae—its microstructures are spines, indicating the converse may also be the case.

Figure 3: Ancestral state reconstruction of the microstructure types of our sample of Cyrtodactylus geckos. * & ** indicate weak and strong transitions towards incipient toepads (lamella-like scales) reconstructed by Riedel et al. (2024). SEM images of microstructures and subdigital scale shapes are illustrated for some species. (Ginal et al. 2026)

The ecotype (e.g., cave, crown, granite, karst) of a species does not predict whether a species has spines, prongs, or setae. However, specific filament traits (e.g., apical diameter, effective bending stiffness) differ significantly among ecotypes—crown‑dwelling species have the smallest apical diameters and the most flexible filaments (lowest effective bending stiffness). Thus, it appears that phylogeny determines what filament type a species has, while micro‑habitat fine‑tunes how those filaments are built.

Overall, our study provides important insight into the evolution of toepads, in that we show that setae (indicative of adhesive competency) can evolve without the expression of obvious macro‑scale pads, and that multiple independent origins of setae have occurred within a single genus. These findings highlight the evolvability of the adhesive system and establishes that the genus Cyrtodactylus offers a living laboratory for the study of the stepwise evolution of complex adhesive systems (thus providing an excellent platform for comparative studies with anoles and other climbing squamates).

If you want to read more, check out our open-access paper:

Ginal, P., Y. Ecker, T. Higham, L. L. Grismer, B. Wipfler, D. Rödder, A. P. Russell, & J. Riedel (2026): Subdigital integumentary microstructure in Cyrtodactylus (Squamata: Gekkota): do those lineages with incipiently expressed toepads exclusively exhibit adhesive setae? Beilstein Journal of Nanotechnology 17: 38–56. https://doi.org/10.3762/bjnano.17.4

Further references:

Riedel, J., K. Eisle, M. Gabelaia, T. Higham, J. Wu, Q. H. Do, T. Q. Nguyen, C. G. Meneses, R. Brown, T. Ziegler, L. L. Grismer, A. P. Russell, & D. Rödder. 2024: Ecologically-related variation of digit morphology in Cyrtodactylus (Gekkota, Squamata) reveals repeated origins of incipient adhesive toepads. Functional Ecology 38: 1630–1648. https://doi.org/10.1111/1365-2435.14597

Garner, A.M. & A.P. Russell, 2021: Revisiting the classification of squamate adhesive setae: historical, morphological and functional perspectives. Royal Society Open Science 8, 202039. https://doi.org/10.1098/rsos.202039

Russel, A. P. (1976): Some comments concerning interrelationships amongst gekkonine geckos. In: D’Bellairs, A., Cox, C. (Eds.), Morphology and Biology of Reptiles. Academic Press, London, pp. 217–244.

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