Climate Does Not Predict Thermal and Hydric Traits in Northern Australian Geckos

1. Reptiles are challenged with maintaining stable hydric states and viable body temperatures in a variable terrestrial environment. Reptiles can use behaviour to select favourable microhabitats as well as physiological adaptations, such as increased skin resistance to water loss to regulate their hydric and thermal states. The degree to which a species’ physiology is adapted to overcome environmental challenges can indicate if species have become specialised to local conditions; for example, reptiles from arid locations tend to have lower rates of evaporative water loss (EWL). 2. EWL rates were measured in 18 species of Australian geckos in the genus Gehyra collected from 11 Northern Territory and Western Australian locations during the dry season, and preferred temperatures were measured for the nine species sampled from the Northern Territory. 3. Rates of EWL did not differ significantly among most species except between a few species with the highest and lowest rates. There was no association between EWL and the aridity of capture locations, and microhabitat conditions (temperature and humidity in rock crevices) did not explain this lack of association. Thermal preferences differed among species, with G. koira selecting significantly cooler temperatures than all other species. Gehyra moritzi, from the most arid location (Kurundi Station), had the highest preferred body temperature, overlapping only with two sympatric species (G. minuta and G. purpurascens). 4. Unlike some reptiles, Gehyra geckos do not specialise in their EWL to match the local climate despite the strong gradient in aridity across sampling sites. Their nocturnal activity and seasonal plasticity in EWL may explain the lack of association between their physiological traits and climate.