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Synopsis In response to rapidly changing environmental conditions, many organisms are experiencing shifts in geographic ranges and in the timing and expression of key life-history traits, which have important effects on fitness. However, the physiological mechanisms that mediate these phenotypic responses, such as endocrine and other signaling pathways are not well understood. This information will be critical for predicting organismal responses to climate change because physiological mechanisms are often highly responsive to environmental cues and influence the phenotypic variation available to selection. Additionally, they often integrate suites of correlated traits and are thus expected to influence the evolutionary response to selection. The overarching goals of this symposium were to gain novel insights into the physiological mechanisms that underlie organismal responses to rapidly changing environmental conditions and to identify gaps in knowledge and experimental approaches to advance the field. Here we review and discuss the symposium contributions and the research themes that emerged as important foci for future studies. 

Abstract Abiotic and biotic factors interact to influence phenotypic evolution; however, identifying the causal agents of selection that drive the evolution and expression of traits remains challenging. In a field common garden, we manipulated water availability and herbivore abundance across 3 years, and evaluated clinal variation in functional traits and phenology, phenotypic plasticity, local adaptation, and selection using diverse accessions of the perennial forb, Boechera stricta. Consistent with expectations, drought stress exacerbated damage from herbivores. We found significant plasticity and genetic clines in foliar and phenological traits. Water availability and herbivory interacted to exert selection, even on traits like flowering duration, which showed no clinal variation. Furthermore, the direction of selection on specific leaf area in response to water availability mirrored the genetic cline and plasticity, suggesting that variation in water levels across the landscape influences the evolution of this trait. Finally, both herbivory and water availability likely contribute to local adaptation. This work emphasizes the additive and synergistic roles of abiotic and biotic factors in shaping phenotypic variation across environmental gradients. 

Summary Herbaceous plant species have been the focus of extensive, long‐term research into climate change responses, but there has been little effort to synthesize results and predicted outlooks. This primer summarizes research on climate change responses for eight intensively studied herbaceous plant species. We establish generalities across species, examine limitations, and propose a path forward. Climate change has reduced fitness, caused maladaptation, and/or led to population declines in at least part of the range of all six forb species. Plasticity alone is likely not sufficient to allow adjustment to shifting climates. Most model species also have spatially restricted dispersal that may limit genetic and evolutionary rescue. These results are surprising, given that these species are generally widespread, span large elevation ranges, and have substantial genetic and phenotypic variation. The focal species have diverse life histories, reproductive strategies, and habitats, and most are native to North America. Thus, species that are rare, habitat specialists, or endemic to other parts of the world are poorly represented in this review. We encourage researchers to design demographic and field experiments that evaluate plant traits and fitness in contemporary and potential future conditions across the full life cycle, and that consider biotic interactions in climate change responses.