Many studies of wild plant species have either detected plastic responses of phenological traits (e.g., flowering time) to experimentally induced or natural climatic variation, or have reported changes in the strength or direction of phenotypic selection in populations occupying different environments.  Few studies, however, have measured the process of adaptive evolutionary change, in real time, in phenological, morphological, or physiological traits. The proposed research will integrate the study of geographic variation in fitness-related traits among populations of a widespread annual herb (Nemophila menziesii, Hydrophyllaceae) with measures of: phenotypic selection on traits that contribute to drought-escape and drought-tolerance; inter-generational change in additive genetic variance in fitness; and the response to selection in order to test predictions regarding adaptation to environmental conditions across an aridity gradient.  We will use the powerful quantitative genetic Aster models to estimate additive genetic variance in individual lifetime fitness in pedigreed populations under field conditions as well as to estimate the strength and direction of selection on phenological, morphological, and physiological traits.  Recent statistical innovations of the Aster model (including the incorporation of random effects) now allow the estimation of genetic variance in lifetime fitness. The intellectual merit of this project includes its application of the Aster model, enabling an empirical evaluation of the accuracy of Fisher’s Fundamental Theorem of Natural Selection, which predicts that the rate of change in population mean fitness should equal the ratio of additive genetic variance in fitness to mean absolute fitness. This ratio represents a population’s capacity to adapt to current conditions, or its "adaptive capacity".  The broader impacts of this project include intensive undergraduate participation and outreach to members of Tribal communities near the targeted study sites.