‘Hanging out’ takes on a new dimension when you're a gecko; clinging onto smooth surfaces with gravity-defying toes, many gecko species are perfectly content to perch at mind-bogglingly steep angles. However, Namib day geckos have taken a different path from their cousins. Preferring to sprint by day at high speeds through the relatively level desert terrain in their foggy coastal home, Rhoptropus afer geckos have lost many of the adhesive features that keep their nocturnal relatives firmly anchored. Explaining that night active geckos rely heavily on vision when navigating their surroundings in the dark, Timothy Higham and Aleksandra Birn-Jeffery at University of California, Riverside, USA, wondered how much of an impact varying light levels might have on R. afer activity when the day begins shrouded in fog that burns off later.
After filming the nimble lizards as they scampered across a sandpaper runway at simulated light levels ranging from complete darkness to a foggy morning to the equivalent of full daylight, Higham and Birn-Jeffery saw the animals sprinting fast (1.4 m s−1) on relatively erect legs in the brightest conditions; ‘Sprinting fast is likely very important for the survival of this species’, the duo says. However, when Higham and Birn-Jeffery turned the lights off, the animals slowed to a more sedate speed (0.6 m s−1), sprawled their legs wide apart and dropped their bodies closer to the ground, leading the duo to suggest that ‘stability may be a significant problem during times when visual input is sub-optimal’. And when they consider the impact that foggy conditions might have on the animals’ mobility, the duo suspects that the geckos have lost the adaptations that benefited the vision of nocturnal ancestors and say, ‘The negative impact of thick fog on light level might cause a corresponding reduction in activity’. They also warn that climate change, which may increase the occurrence of fog, could limit the ability of the fleet-footed geckos to forage in the dimmer conditions.
