Meta-analysis reveals the tempo of evolutionary parallelism of local adaptation between native and introduced ranges of plant species

Invasive species are valuable systems for evaluating evolutionary predictability, as populations in native and introduced ranges evolve separately, yet often encounter similar environmental challenges that select for parallel patterns of local adaptation. However, it remains unclear how pervasive and strong such parallelism is and how rapidly it evolves. To address these questions, we first extended cline theory to predict evolutionary patterns of parallelism between ranges. We then carried out a meta-analysis of clinal divergence in native and introduced populations of the same plant species and evaluated the tempo of evolutionary parallelism between ranges. Clines in introduced ranges were, on average, slightly shallower than native range clines for size, morpho-physiology, and phenology traits, but similar for reproductive and defense traits. Evolutionary parallelism of clinal divergence strongly increased with the time since introduction, with the greater parallelism in older introductions primarily caused by increased alignment in the direction of clinal divergence between ranges rather than changes in their relative magnitudes of divergence. These results are consistent with a two-phased process of cline evolution, in which introduced clines initially arise by drift during the range expansion, and subsequently evolve in response to local selection, ultimately leading to strong parallelism with the native range.