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

Abstract

Abstract Sister species that live in sympatry provide the possibility to analyse the level of divergence in their ecological, physiological and life-history traits and how they can coexist without out-competing each other. We studied the thermal sensitivity of locomotor performance in the sympatric lizards Phymaturus querque and Phymaturus zapalensis from Patagonia, Argentina. We measured morphological traits relevant to locomotor performance and the running speed at different body temperatures, and we estimated the critical thermal minimum (CTmin) and maximum (CTmax) at which running performance equals zero. We obtained the maximum speeds, the temperature at which the performance is maximized (optimal temperature, To) and the temperature range over which an individual performs 50% and 80% of their maximal performance (B50 and B80). Also, we recorded the availability of thermal microenvironments for thermoregulation (operative temperatures) and calculated two indices of vulnerability to global warming. Phymaturus zapalensis and P. querque exhibited differences in most of the morphological traits relevant to locomotor performance. Both species presented similar values of To, CTmin and CTmax, but B50 and B80 were broader in P. zapalensis. During the warmest month, the environmental temperatures are already higher than the physiological optimal temperature, indicating that populations could currently be facing challenges in the context of global warming.