General patterns and predictors of thermal tolerance in bees: A global synthesis across taxa and environments

Understanding how organisms respond to temperature variation has become central to ecology and evolution because of its role in shaping species' physiology, distribution, and ecological interactions. Thermal tolerances are critical for ectothermic organisms, which have evolved a variety of behavioral and physiological strategies to manage thermal stress that vary widely across geographic and temporal scales. This study synthesizes existing information on bees' critical thermal maximum (CT_max) and minimum (CT_min) through a systematic review of published data. Despite bees' ecological importance, research on such common metrics of thermal tolerance remains scarce, with fewer than 50 accumulated studies over the past 30 years and less than 1% of species represented. Data are biased to North America, especially the USA, Oceania and Europe, leaving vast regions unexplored. We found that CT_max was correlated with variables related to body size and ramping rates during measurement, but not with mean, maximum and minimum temperatures; CT_min correlated only with the coldest month's minimum temperature and mean annual temperature. These patterns underscore the role of local climate in shaping thermal adaptation. However, major knowledge gaps persist, limiting predictions of climate change impacts. We call for broader studies on intra-specific thermal tolerance variation across geography, life stages, and social traits to predict climate change impacts and guide bee conservation.