Seasonality, microclimate, or macroclimate: What governs the plasticity of ant thermal tolerance?

Global warming poses a significant threat to insects, which play indispensable roles in terrestrial ecosystems, and whose body temperatures closely track those of their habitats. Most large-scale predictions about insect distribution and resilience to climate change rely on air temperature data taken 2-m above the ground. However, such macroclimate data often fail to represent the temperatures experienced by ground foraging insects. Insects are also exposed to substantial temperature variations across seasons, especially in temperate regions, which can drive acclimatization of thermal limits. This thermal plasticity may be crucial for withstanding global warming as it allows insects to rapidly adjust their thermal tolerance. To disentangle the effects of spatial and temporal temperature variation on thermal tolerance, we studied Mediterranean ant populations from two climatically distinct localities. We measured thermal tolerance across the most common species to understand the effect of macroclimate, microclimate, and seasonality on the plasticity of heat and cold tolerance. We found greater variability in cold tolerance across both microclimates and seasons, even within the hot Mediterranean climate. Seasonality was the best predictor of thermal tolerance indicating that temporal temperature variation currently drives most of the observed thermal plasticity in this biodiversity hotspot. Our findings suggest that thermal tolerance data from temperate regions should be used cautiously in macrophysiological studies, as temporal variation in physiological traits may be more pronounced than spatial temperature gradients.