Thermal dependence of locomotor performance in two cool-temperate lizards

Temperate-zone ectotherms experience varying or very low ambient temperatures and may have difficulty in attaining preferred body temperatures. Thus, adaptations to reduce the thermal dependence of physiological processes may be present. We measured the optimal temperature range for sprint speed and compared it with the selected body temperatures (T_sel) of two sympatric, cool-temperate lizards: the diurnal skink Oligosoma maccanni and the primarily nocturnal gecko Woodworthia (previously Hoplodactylus) ‘‘Otago/Southland’’. We also investigated whether time-of-day influenced sprint speed. Contrary to results for other reptiles, we found that time-of- day did not influence speed in either species. For each species, the optimal temperature range for sprinting and T_sel overlapped, supporting the ‘thermal coadaptation’ hypothesis. However, the optimal range of temperatures for speed is not always attainable during activity by either species, which have limited opportunities to attain T_sel in the field. The thermal sensitivity of sprint speed in these two species does not appear to have evolved to fully match their current thermal environment. More data on cold- adapted species are needed to fully understand physiological adaptation in ectotherms.