title: Light level impacts locomotor biomechanics in a secondarily diurnal gecko, Rhoptropus afer.
abstract: Locomotion through complex habitats relies on the continuous feedback from a number of sensory systems, including vision. Animals face a visual trade-off between acuity and light sensitivity that depends on light levels, which will dramatically impact the ability to process information and move quickly through a habitat, making ambient illumination an incredibly important ecological factor. Despite this, there is a paucity of data examining ambient light in the context of locomotor dynamics. There have been several independent transitions from the nocturnal ancestor to a diurnal activity pattern among geckos. We examined how ambient light level impacted the locomotor performance and high-speed three-dimensional kinematics of a secondarily diurnal, and cursorial, gecko (Rhoptropus afer) from Namibia. This species is active under foggy and sunny conditions, indicating that a range of ambient light conditions is experienced naturally. Locomotor speed was lowest in the 'no-light' condition compared with all other light intensities, occurring via a combination of shorter stride length and lower stride frequency. Additionally, the centre of mass was significantly lower, and the geckos were more sprawled, in the no-light condition relative to all of the higher light intensities. Locomotor behaviour is clearly sub-optimal under lower light conditions, suggesting that ecological conditions, such as very dense fog, might preclude the ability to run quickly during predator-prey interactions. The impact of ambient light on fitness should be explored further, especially in those groups that exhibit multiple transitions between diel activity patterns.
authors.affiliation: William Harvey Research Institute, Centre for Sports and Exercise Medicine, Queen Mary University London, London E1 4DG, UK a.birn-jeffery@qmul.ac.uk.|Department of Biology, University of California, Riverside, CA 92521, USA.
authors.forename: Aleksandra V
authors.initials: AV
authors.lastname: Birn-Jeffery
authors.affiliation: Department of Biology, University of California, Riverside, CA 92521, USA.
authors.forename: Timothy E
authors.identifier: 0000-0003-3538-6671
authors.initials: TE
authors.lastname: Higham
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena / Q000528:radiation effects; D001835:Body Weight; D002940:Circadian Rhythm / Q000528:radiation effects*; D005552:Forelimb / Q000502:physiology; D006614:Hindlimb / Q000502:physiology; D008027:Light; D008116:Lizards / Q000502:physiology*; D008124:Locomotion / Q000528:radiation effects*; D012044:Regression Analysis; D062211:Spatio-Temporal Analysis
keywords: Desert; Fog; Gekkonidae; Kinematics; Lizard; Locomotion; Performance; Stability; Vision; Visual acuity