Variation in thermal biology of three closely related lizard species along an elevation gradient

The critical thermal limits of organisms and the thermal sensitivity of their performance tend to vary predictably across latitudinal gradients. There has been comparatively less investigation into variation in thermal biology with elevation, despite similar gradients in environmental temperatures. To redress this, we examined critical thermal limits (CTmin and CTmax), thermal sensitivity of locomotor performance, and shelter site attributes, in three lizard species that replace one another along a contiguous elevation gradient in south-eastern Australia. The species examined consisted of a highland specialist, Liopholis guthega, mid-elevation species, Liopholis montana, and lowland species, Liopholis whitii. We found similar habitat attributes between the species, but L. guthega predominantly occurred in open habitat, which might reflect a strategy for maximizing exposure to insolation. We found intraspecific variation in lizard thermal traits, most notably in cold tolerance of L. guthega and in both heat and cold tolerance of L. whitii, suggesting population-specific variables acting on thermal physiology rather than a species distribution maintained by distinct thermal tolerances. This study represents one of the few examinations of thermal trait variability within and between species with elevation in a temperate system and provides evidence for thermal physiology driven by adaptation and/or physiological plasticity to local conditions.