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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, T o) and the temperature range over which an individual performs 50% and 80% of their maximal performance (B 50 and B 80). 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 T o, CTmin and CTmax, but B 50 and B 80 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. [ABSTRACT FROM AUTHOR]

The Puyehue-Cordón Caulle eruption of 4 June 2011 dispersed about 100 million tonnes of pyroclastic materials resulting in ash accumulations of 30 cm depth on the Patagonian steppe, an area occupied by several lizard species. Herein we analysed, by experimental trials, the effects of ash and slope on running performance of two endemic and vulnerable species, Phymaturus excelsus and Phymaturus sinervoi, restricted to volcanic rock outcrops in Patagonia. We also determined the effect of ash fall on body condition by comparing the same populations before and after the volcanic eruption. Locomotion of P. excelsus, adapted to rocky and steep outcrops, was more affected in a negative way by ash. In contrast, P. sinervoi, which lives in mixed habitats with flat rocks and sandy substrates, ran more slowly on the inclined surface but was unaffected by ash, suggesting the two species are well adapted to the habitats they occupy. In spite of impacts of ash deposition on locomotion and potentially the feeding, reproduction and dispersal activity of P. excelsus, lizards captured 18 months after ash deposition showed improved body condition. Our study site for P. sinervoi received less ash deposition and hence body condition was similar before and after ash fall. We hypothesize that negative effects of ash on lizards were counteracted by competitive release; ash deposition caused an acute and significant increase in mortality of herbivorous competitors such as hares and sheep that feed upon the same flowers and fruits included in the Phymaturus diet. [ABSTRACT FROM AUTHOR]