Living in Hot Sand: The Thermal Biology of Scincus scincus, the Sandfish Skink

Little is known about the natural history of Sandfish Skinks (Scincus scincus), despite a range spanning two continents. In arid and hot environments across North Africa and the Arabian Peninsula, these lizards are uniquely adapted to a sand dune environment. However, much about the basic biology of this species remains unknown, especially concerning adaptations to its thermal environment. With this study, we compiled a robust suite of thermal biology parameters to assess within-individual trait covariation in Sandfish Skinks (n = 8). We found one of the highest recorded critical thermal maxima for a vertebrate ectotherm (mean: 48.2 °C), suggesting a large thermal safety margin. We quantified thermal preferences and documented use of sand horizons to thermoregulate. We monitored individual body temperatures day and night for one week and found significant differences in active and inactive thermoregulation. Additionally, we quantified thermal dependence of performance by recording sprinting speed and diving speed, important for prey capture and predator avoidance, across a range of temperatures. Finally, we measured the critical thermal minimum (CTMIN) and maximum (CTMAX), allowing us to build a complete thermal performance curve (TPC) for two behaviors, which we used to estimate optimal temperatures for performance. We then tested the relationship between thermal preferences and performance, finding no support for the thermal coadaptation hypothesis in the context of hunting or predator avoidance. Overall, these data provide understanding of how this unique ectotherm survives in the extreme thermal conditions of a hot desert.