The theory of evolutionary processes acting within species (microevolution) is more mature than that for macroevolution, but there is surprisingly little evidence of divergent natural selection on physiological traits under natural conditions. To redress this gap, I am collaborating with Amy Angert (UBC) to investigate the physiology of local adaptation to climate in Mimulus cardinalis. We want to know what physiological traits are involved in climatic adaptation, what climatic factors shape local adaptation, and how does local adaptation affect heritable variation in fitness? Answering the last question will provide key parameter estimates for predicting whether species can adapt to rapid climate change. We have found latitudinal clines in physiological traits which suggest local adaptation to climate (Muir & Angert 2017), and are now using reciprocal transplants between Northern and Southern locations in California to measure physiological local adaptation under ecologically realistic field conditions.