Preferred body temperatures are increasing in 3 anguimorph lizards with passive thermoregulation

Rising environmental temperatures and extreme climatic events are negatively affecting ectothermic animals, especially those with limited opportunities for behavioral thermoregulation (i.e., passive thermoregulators). Rather than rely on behavioral buffering, thermally passive ectotherms may instead adjust their thermal preferences (either lowering or increasing them) to perform their biological activities at warmer temperatures. Nevertheless, temporal comparisons of preferred temperatures in wild populations of passive thermoregulators remain scant, limiting our capacity to broadly anticipate their responses to rising temperatures. Here, we compared laboratory thermal preferences across years (2003-2004 vs. 2016-2018) in 3 thermally passive lizard species from Central Mexico: the anguimorphs Gerrhonotus liocephalus, Xenosaurus rectocollaris, and X. tzacualtipantecus. These species exhibit different habitat use and live in places where heat wave events have increased over time, allowing temporal comparisons of thermal preferences in warming habitats. We discovered that the 3 species increased their thermal preferences by ∼1°C in 12-15 years. Our results indicate that these, and likely other passive thermoregulators must adjust their thermal preferences in response to global warming, rising a profound concern about their long-term viability as they approach intrinsic limits in their thermal physiology.