Discussion:
We found evidence of selection acting on both traits and trait plasticity across our three common gardens. In addition, regressions between traits and provenance climate indicate that much of the selection detected with QST-FST analysis is driven by climatic clines to which these populations are locally adapted. The result of mostly high QST values for traits is consistent with a majority of studies finding QST is generally larger than FST for ecological traits (McKay & Latta 2002; Savoleinen et al. 2007; Leinonen et al.2013). However, our result of divergent selection acting on trait plasticity is quite striking in light of the relatively few examples of selection on plasticity documented in the literature (Arnold et al. 2019). Combining QST-FST analysis on trait plasticity with plasticity-climate regressions can help uncover the evolutionary forces shaping plasticity differences across environmental gradients (Whitlock 2008; Josephs 2018; Kelly 2019). Below, we discuss the evidence for climate-driven adaptive divergence in traits and trait plasticity, local adaptation to climate, and the potential consequences of both under current climate change.