Abstract

Terrestrial animals constantly move in complex habitats that vary both spatially and temporally. The characteristics of these habitats are not only defined by the physical environment, but also the photic environment even though the latter has largely been overlooked. Numerous studies of terrestrial locomotion have examined the role of habitat structure, such as incline, perch diameter, and compliance, on running performance, yet the role of the photic environment is vastly understudied. Geckos are an exceptional group for analyzing the role of the photic environment on locomotion as they exhibit several independent shifts to diurnality from a nocturnal ancestor, they are visually-guided predators, and they are extremely diverse. Our initial goal is to discuss the range of photic environments that can be encountered in terrestrial habitats, such as day versus night, canopy cover in a forest, fog, and clouds. We then review the physiological optics of gecko vision with some new information about retina structures, the role of vision in motor-driven behaviors, and what is known about gecko locomotion under different light conditions, before demonstrating the effect of light levels on gecko locomotor performance. Overall, we highlight the importance of integrating sensory and motor information and establish a conceptual framework as guide for future research. Several future directions, such as understanding the role of pupil dynamics, are dependent on an integrative framework. This general framework can be extended to any motor system that relies on sensory information, and can be used to explore the impacts of performance features on diversification and evolution.