Lizards on ice: Comparative thermal tolerances of the world's southernmost gecko

(1) We measured thermal tolerances (critical thermal minimum, CT_min and panting threshold, T_pant) for four populations of Homonota darwinii spanning most of the latitudinal range of the species. (2) CT_min differed across populations, but not latitudinally as predicted, likely because latitude was not as good a proxy for operative temperatures (T_e). (3) Some populations had subzero CT_min indicating supercooling or freeze tolerance—the first time either phenomenon has been reported for a gecko. (4) T_pant did not differ significantly among populations. (5) The thermal tolerance breadth appears to be correlated with thermal variability in the environment. (6) Annual T_e data indicate gecko retreats play a crucial role in surviving extreme surface temperatures (<0 or >50 °C).