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 across each range. 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 trait cline 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 trait cline parallelism between ranges. We found that clines in introduced ranges were somewhat shallower than native range clines, and directions of clinal divergence were, on average, partially aligned between ranges, with extensive variation in parallelism among traits and species, including counter-clines between native and introduced ranges. The degree of evolutionary parallelism of clinal divergence strongly increased, and the prevalence of counter-clines decreased, with the time since introduction, where greater parallelism in older introductions was primarily caused by increased alignment in the direction of clinal divergence between ranges rather than changes in their relative magnitudes of divergence. We argue that these observations are consistent with a two-phased process of cline evolution across introduced ranges. In the first phase, misaligned clines between introduced and native ranges can arise during range expansions, often owing to demographic and genetic constraints that initially hinder the evolution of local adaptation within the new range. During the second phase, the evolution of local adaptation eventually resolves early instances of maladaptation across introduced ranges, leading to strong trait cline parallelism between native and introduced ranges.