ABSTRACT
Urbanization has caused regional increase in temperatures that exceed those measured on a global scale, leading to urban heat islands, as much as 12°C hotter than their surroundings. Optimality models predict that ectotherms in urban areas should tolerate heat better and cold worse than ectotherms in rural areas. We tested these predications by measuring heat and cold tolerances of leaf-cutter ants from South America’s largest city (São Paulo, Brazil). Specifically, we compared thermal tolerance of ants from inside and outside of the city. Knock-down resistance and chill-coma recovery were used as indicators of heat and cold tolerances, respectively. Ants from within the city took 20 percent longer to lose mobility at 42°C than ants from outside the city. Interestingly, greater heat tolerance came at no obvious expense of cold tolerance; hence, our observations support the current theory only partially. Our results indicate that thermal tolerances of some organisms can respond to rapid changes in climate. Predictive models should account for acclimatory and evolutionary responses during climate change.
