Comparative thermal sensitivity of locomotor performance and vulnerability to global warming of two sympatric Phymaturus lizards from cold environments of Patagonia (Argentina).

This article focuses on the thermal sensitivity of locomotor performance in two sympatric lizard species, *Phymaturus querque* and *Phymaturus zapalensis*, from Patagonia, Argentina, and assesses their vulnerability to global warming. Despite significant morphological differences, both species exhibited similar critical thermal minimum and maximum temperatures (CTmin and CTmax), optimal temperatures for locomotion (To), and maximum running speeds, though *P. zapalensis* showed a broader thermal performance breadth (B50 and B80), indicating greater flexibility across temperatures. Environmental temperatures during the warmest month already exceed the species' optimal temperatures, suggesting current challenges related to climate warming, with both species relying on thermal refuges such as rock crevices. The study implies that *P. zapalensis*' broader thermal tolerance and less precise thermoregulation may allow longer daily activity and coexistence with the larger, more territorial *P. querque*, but both species face potential fitness and survival risks under ongoing temperature increases.