Natural selection contributes to geographic patterns of thermal plasticity in Plantago lanceolata.

A long-standing debate in evolutionary biology concerns the relative importance of different evolutionary forces in explaining phenotypic diversification at large geographic scales. For example, natural selection is typically assumed to underlie divergence along environmental gradients. However, neutral evolutionary processes can produce similar patterns. We collected molecular genetic data from 14 European populations of Plantago lanceolata to test the contributions of natural selection versus neutral evolution to population divergence in temperature-sensitive phenotypic plasticity of floral reflectance. In P. lanceolata reflectance plasticity is positively correlated with latitude/altitude. We used population pairwise comparisons between neutral genetic differentiation (FST and Jost's D) and phenotypic differentiation (PST) to assess the contributions of geographic distance and environmental parameters of the reproductive season in driving population divergence. Data are consistent wi...