Leaf size, shape, and internal anatomy are extremely diverse but strongly constrained by functions such as light interception, CO$_2$ diffusion, and managing scarce resources like water and nitrogen. Two common assumptions are that plants i) cannot build tougher leaves without sacrificing photosynthesis and ii) cannot increase photosynthesis without decreasing water-use efficiency. In collaboration with physiologist Jeroni Galmés (UIB, Spain), I have shown that in contrast to (i) increased leaf toughness (higher leaf mass per area) weakly constrains the evolution of photosynthetic function among closely related species (Muir et al.
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?