Abstract

Autumn, K., Weinstein, R. and Full, R.J. 1994. Low cost of locomotion increases performance in a nocturnal gecko. Physiol. Zool. 67, 237-261

Thermal optima for physiological processes are generally high (30° -40° C) in lizards. Performance decreases substantially at low temperatures, yet some lizards are nocturnal and are active with body temperatures. below 15° C. We corroborated three hypotheses about the ecophysiological consequences of the evolution of nocturnality in lizards: (1) nocturnality requires activity at low temperature; (2) activity at low temperature imposes a thermal handicap that constrains performance capacity; (3) nocturnal species have higherperformance capacity at low temperature than do comparable diurnal species. Field body temperatures during activity averaged 15.3°C in Teratoscincus przewalskii, a nocturnal, terrestrial gecko from northwestern China. Individuals of T. przewalskii sustained exercise at 15°C on a treadmill for more than 60 min at 0.18 km/h. However, 15°C was suboptimalfor sustained locomotion. Resting and maximum oxygen consumption at 15° and 25° C were similar to predicted values for diurnal lizards, supporting the hypothesis that much of thermal physiology in lizards is evolutionarily conservative. The minimum cost of transport (Cmin, O. 73 mL O2/g /km) for T. przewalskii was only 3496 of the predicted value for a diurnal lizard of the same mass. This low cost yielded a maximum aerobic speed (MAS) of 0.27 km/h at 159° C, which is 2.5 times the predicted MAS for a diurnal lizard of the same mass. In comparison with predicted values for diurnal lizards, T. przewalskil showed increased but thermally submaximal 1ocomotor performance capacity at nighttime temperatures.