SYNOPSIS. The plasticity of any given trait, which has a genetic basis and which may or may not be adaptive, can intensify or attenuate evolved responses, and can itself evolve in response to selection depending on the scale of spatial or temporal heterogeneity. To investigate the complex function and evolution of plastic traits, an appealing yet challenging approach is assessing responses to artificial selection. Here, I review how artificial selection has been employed to explore four

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... l research themes: (1) relationships between plastic and evolved responses to multiple stresses, (2) integration of cellular, leaf-level, and whole-plant responses to altered CO 2 concentrations, (3) photomorphogenic and photoperiodic development, both mediated by phytochrome photoreceptors, and (4) the evolution of the pest-induced myrosinase-glucosinolate system in cruciferous plants. These diverse topics are unified not only because they have been studied using artificial selection experiments, but also because they have considered variability in multiple traits affected by multiple factors in the external environment. Limitations of such research include a dearth of long-term studies; a surprising but often logistically necessary omission of control or replicate lines; and numerous issues relating to assessing impacts of inbreeding and drift. In addition to discussing options for circumventing such limitations, I draw attention to strategies for integrating the results of artificial selection studies with progress in functional and evolutionary genomics.