Colony-level mechanisms of thermal tolerance regulation in the ant Ectatomma ruidum

1. Insects spend energy to function in high temperature environments, and because social insects employ a division of labor, it is likely that thermal tolerance varies among individuals in the colony, based on the tasks that they perform. 2. Foraging workers of the ant Neotropical ant Ectatomma ruidum are known to show temporal differences in thermal tolerance, with greater tolerance in hot afternoons, relative to cool mornings. 3. We developed three hypotheses that can account for temporal differences in thermal tolerance among workers: Thermal Acclimation, Division of Labor, and Circadian Rhythm. 4. We tested these hypotheses with a pair of experiments that involved the measurement of thermal persistence of ants at a constant temperature in time-to-failure assays. The first experiment compared ants with different behavioral roles in colonies, and the second compared colonies subjected to thermal manipulations, then iteratively sampled at daily thermal maxima and minima. 5. We found robust support for the Circadian Rhythm and Thermal Acclimation Hypotheses, and little support for the Division of Labor Hypothesis. Colonies of this species integrate multiple mechanisms of adapting to thermal challenges including time of day, ambient temperature, and the behavioral context of individual workers.