Nesting behaviour drives the evolution of heat tolerance and climate vulnerability in bees

Species’ vulnerability to climate change depends on their capacity to evolve in response to increasing heat as climates change ¹ . But, weak signatures of adaptation in heat tolerance across environments make it difficult to predict species evolutionary responses ^2–4 . These weak signatures could reflect a lack of consideration of species behaviour and the corresponding micro-climates they inhabit. We examined heat tolerance in 95 species of wild bees — among the most important pollinators on Earth — across the latitudinal extent of Australia. We found that nesting behaviour (plant stem, wooden cavity, or ground), which impacts the micro-climate species are exposed to, predicted species’ heat tolerances. We demonstrate that nesting behaviour influences the mode of selection on heat tolerance, such that species with different nesting behaviours evolve towards discrete thermal optima independently of phylogeny. This is the first example of repeated evolution of heat tolerance depending on behaviour. Finally, models that consider nesting behaviour change the rank order of which species are most at risk to climate change. Our results underscore the need to understand the drivers of heat tolerance evolution across species to better identify the taxa most at risk to climate change.