Ant Thermal Tolerance: A Review of Methods, Hypotheses, and Sources of Variation

Abstract Ants (Hymenoptera: Formicidae) are a conspicuous group of ectotherms whose behavior, distribution, physiology, and fitness are regulated by temperature. Consequently, interest in traits like thermal tolerance that enable ants to survive and thrive in variable climates has increased exponentially over the past few decades. Here, we synthesize the published literature on the thermal tolerance of ants. We begin our review with discussion of common metrics: critical thermal limits, lethal thermal limits, knock-down resistance, chill-coma recovery, and supercooling. In particular, we highlight the ways each thermal metric is quantified and offer a set of methodological caveats for consideration. We next describe patterns and hypotheses for ant thermal tolerance along spatial and temporal temperature gradients. Spatially, we focus on relationships with latitude, elevation, urbanization, and microclimate. Temporally, we focus on seasonal plasticity, daily variation, dominance-thermal tolerance tradeoffs, and acclimation. We further discuss other sources of variation including evolutionary history, body size, age, castes, and nutrition. Finally, we highlight several topics of interest to ant thermal biologists, ranging in scope from methods development to the impacts of climate change.