Unveiling Critical Thermal Limits of Anolis tolimensis (Squamata, Anolidae) across an Elevational Landscape

Abstract

Northern Andes Mountains exhibit high elevational fluctuation in thermal conditions for ectotherms. This fluctuating temperature limits the survival, growth, and dispersion of ectothermic organisms. Therefore, lizard species distributed on these mountain landscapes face strong temperature fluctuations. To test the potential effect of elevation, we characterized the critical maximum (CT_max) and minimum (CT_min) body temperature and time to reach CT_max (T_max) and CT_min (T_min) of individuals of Anolis tolimensis, an endemic species distributed on two cordilleras in the northern Andean system in Colombia. We collected individuals at four elevations (1,600, 1,900, 2,100, and 2,200 m asl) and measured their critical thermal limits under laboratory conditions. We also explored the role of sex and size on these physiological thermal variables. CT_max is similar among the elevations, but CT_min of the highest elevation (2,200 m asl) is the lowest (5.5±1.0°C) vs (2,100 m asl, 8.8±0.8°C; 1,900 m asl, 8.3±1°C; 1,600 m asl, 8.3±0.9°C). CT_max range is narrower (33–34.2°C) than CT_min (5.5–8.8°C), and thermal tolerance breadth (CT_min to CT_max values) is 28.7°C. Sex and body size may affect the thermal response, but the interaction varies with geography. Critical thermal limits are conservative (CT_max) or evolutionary labile (CT_min). Anolis tolimensis could deal with maximum environmental temperatures by thermoregulatory behavior or by an alternative strategy of increasing the time to reach the CT_max. Finally, extinction risk evaluation is needed to test the potential vulnerability of the population at the second-highest elevation.