Heat and water loss vs shelter: a dilemma in thermoregulatory decision-making for a retreat-dwelling nocturnal gecko

Understanding the interaction between upper voluntary thermal limit (VTmax) and water loss may aid in predicting responses of ectotherms to increasing temperatures within microhabitats. However, the temperature (VTmax) at which climate heating will force cool-climate, nocturnal lizards to abandon daytime retreats remains poorly known. Here, we developed a new laboratory protocol for determining VTmax in the retreat-dwelling, viviparous Woodworthia Otago/Southland gecko, based on escape behaviour (abandonment of heated retreat). We compared the body temperature (Tb) at VTmax, and duration of heating, between two source groups with different thermal histories, and among three reproductive groups. We also examined continuous changes in Tb (via an attached biologger) and total evaporative water loss (EWL) during heating. In the field, we measured Tb and microhabitat thermal profiles to establish whether geckos reach VTmax in nature. We found that VTmax and duration of heating varied between...