Thermal effects on locomotion in the nocturnal gecko Homonota darwini (Gekkonidae)

Nocturnal lizards show a complex adaptation to environmental temperature. They obtain heat from the substratum, using daytime for performing physiological functions inside thermally suitable shelters, and night-time which involves locomotion and loss of heat for capturing prey. Homonota darwini, the southernmost geckonid in the world, is a small nocturnal insectivorous gecko that occurs in saxicolous habitats of Patagonia, Argentina. Geckos were captured by hand during the day on a rocky hill near Bariloche (Río Negro, Argentina) in spring and summer. All the geckos were active during daytime and had good limb mobility with a median body temperature of 23°C. Body temperatures showed a direct dependence on the temperature of the roof of the shelter and on the air temperature. Geckos were made to run on a horizontal track and running speed was measured in two experiments: long runs (1 m) and sprint runs (0.20 m) during the day (diurnal) and at night (nocturnal). Speed was significantly greater in sprints than in long runs and speed increased with body temperature, reaching a maximum at a body temperature of 22°C. Thus, we conclude that, although the low temperatures of Patagonia impose heavy constraints on the physiological performance of Homonota darwini, they have a peculiar arrangement of mechanical and biochemical abilities which allows for resource acquisition at night, using cryptic habits and short sprint runs.