Knock-down resistance to heat stress of Atta cephalotes in urban environments

Temperature is one of the main environmental factors affecting all living organisms, impacting survival and reproduction. In cities, the speed of urbanization is associated with an increase in temperatures and leads to the creation of urban heat islands (UHIs). In the tropics, the temperature differential between urban and rural zones can reach up to 12 °C, a condition that might favour the spread of some insect species due to their ability to adapt to high temperatures. In this study, we evaluated the plasticity of the ant Atta cephalotes when the temperature increases due to the UHI effect. A total of 8000 ants were collected from two different zones (inside the UHI and outside the UHI) in the city of Cali, Colombia. Five different temperatures were tested using an environmental chamber, ranging from 38 to 42 °C in 1 °C increments. Knock-down was recorded when ants ceased to move. A linear mixed model and Cox model with mixed effects were used to test the knock-down time and probability of survival at the treatment temperatures. Although no clear differences were found between the two zones, this study reveals for the first time the capacity of A. cephalotes to tolerate high basal temperatures regardless of the environment. This represents evidence of the high basal thermotolerance of this ant species to thermal stress in tropical UHI environments.