| Physiological variation is often assumed to be adaptive based on broad correlations with environmental resource gradients. However, these adaptive assumptions are rarely tested by examining the direct impact of physiological variation on fitness in natural populations. Using phenotypic selection, I tested whether photosynthetic and stomatal traits responded adaptively to wet and dry environments in greenhouse populations of Avena barbata. I found that selection on most physiological traits was strong in the wet environment. In contrast, many of the adaptive predictions of physiological variation under drought were not supported. I also assessed potential genetic constraints on adaptive evolution of these photosynthetic and stomatal traits. I found that most traits had higher heritable variation in the dry environment; however, there were also more genetic correlations between the traits. Although there was stronger selection on physiological traits under wet conditions, the response to selection pressures may be faster under dry conditions. |
