Geckos running with dynamic adhesion: towards integration of ecology, energetics and biomechanics

Morphological specializations often enable animals to deal with challenges in nature, a prime example being the adhesive system of geckos. With this, geckos can access smooth and vertical (and even inverted) areas of the habitat that most other animals cannot. However, what is known about how geckos cling stems primarily from laboratory studies of static adhesion, with an emphasis on the integumentary component of the adhesive apparatus. In reality, the system is hierarchical, with complex musculotendinous, vascular and sensory systems that are crucial for achieving attachment, modulation of attachment strength and ultimately, detachment. Experiments examining these additional components are virtually non-existent. Additionally, there is a paucity of information about the surfaces on which geckos move, how geckos move in their natural habitat and how the adhesive system is controlled during running over complex surfaces. It is unclear whether having an adhesive system reduces the energetic costs of running compared with lizards that lack the system. We propose a complimentary set of laboratory and field studies to fill major gaps in our understanding of gecko adhesion and locomotion. Key outstanding questions are: (1) How does surface structure influence locomotion? (2) How might geckos modulate adhesion through physiological mechanisms? (3) How do geckos locomote in complex natural habitats that vary in structural properties? (4) What are the underlying energetic costs of moving dynamically in nature with an adhesive system? We address these questions and generate a roadmap for future work, including the framing of testable hypotheses. The results of such studies will help us to understand the evolution of fast locomotion in small ectothermic vertebrates and the energetic costs of moving in complex habitats. In addition, they may inform the development of small adhesive robots.