A selection of gecko toepads. Top: Gekko gecko by Peter Geissler, left: Pseudothecadactylus australis by Nick Weiger, right: Oedura monilis by Rishab Pillai.
Like in Anolis lizards, the evolution of adhesive toepads in geckos is often seen as a key innovation, allowing these lizards to exploit vertical environments. Gecko toepads are among the most advanced in the animal kingdom – inspiring research in biomimetics and synthetic adhesion for years. Yet, while the physics of sticking has been studied extensively, the ecology and biogeography have not. Most studies focus on morphology and performance in single species or genera, while large-scale ecological analyses have been rare, something that is considered as a major gap in the literature.
That’s where our project began. The idea originated with Assoc. Prof. Dr. Dennis Rödder and Dr. Jendrian Riedel, and the first task was to take a broad-scale look at toepad variation across all geckos. Following the classification system of Russell and Gamble (2019), we categorized every species into one of four types – absent toepads, basal, distal, and fanlike (Fig. 1) – each morphologically distinct while their functional differences are still not fully understood.
Fig. 1: The four toepad categories according to Russel and Gamble (2019). Ventral view of digit IV from representative species: Left pes of Cyrtodactylus khasiensis (absent), right pes of Gekko smithii (basal), left pes of Ebenavia inunguis (distal), and left pes of Uroplatus ebenaui (fanlike). Illustrations modified from Riedel et al. (2024) and Russell and Gamble (2019).
To explore their evolution and geographic distribution, we combined toepad data with open-access resources on species ranges, phylogeny, climate, and habitat types. Following a range of analyses, we decided on some of the most significant results to create the story-line for our publication.
The first valuable contribution is the classification of toepad types across all species (2230 at the time, excluding the limb-reduced pygopodids), data that is now freely available (Fig. 2). In combination with the phylogeny, we confirmed multiple independent gains of toepads and propose a differential pathway of transitions between pad types.
Fig. 2: Species numbers and family distribution across toepad categories. Includes all recent non-limb-reduced Gekkota species as of September 30 2023 (2230 species)(Kukla et al. 2025, Supplement).
Linking this dataset with biogeography and macro-climate, we also examined how different toepad types are distributed across the globe (Fig. 3) and how they relate to climate and habitat use. Interestingly, we found no sharp climatic boundaries between pad types. Instead, global patterns seem to reflect biogeographic history and the environments where geckos diversified. Nevertheless, we see some habitat associations: adhesive pads tend to show up in structurally complex environments like rocky areas, forests, and even urban settings.
Fig. 3: Global species richness maps for each toepad category: (A) absent, (B) basal, (C) distal, (D) fanlike (Kukla et al. 2025).
Overall, our study provides a global overview of toepad diversity and offers a framework for future, finer-scale studies, moving from global biomes to local microhabitats. We show that gecko diversity isn’t just about sticking to surfaces, it’s about how evolution, ecology, and geography stick together to shape the incredible variety of forms we see today.
If you want to read more, check out our open-access paper: