Interannual variation in season length is linked to strong co-gradient plasticity of phenology in a montane annual plant

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Ensing, David J.
Eckert, Christopher G
co-gradient plasticity , elevation , genetic differentiation , range limit , reciprocal transplant , reproductive phenology , Rhinanthus minor , season length
Species are commonly distributed along latitudinal and elevational gradients of growing season length to which they might respond via phenotypic plasticity and / or adaptive genetic differentiation. However, the relative contribution of these processes and whether plasticity, if it occurs, facilitates expansion along season length gradients remains unclear but are important for predicting species fates during anthropogenic change. We quantified phenological trait variation in the montane annual Rhinanthus minor for three generations at 12 sites across 900 m of elevation in the Canadian Rocky Mountains and conducted a reciprocal transplant experiment for two generations among nine sites. We compared clines and interannual variation of phenological traits between natural and transplanted individuals. Season length declined by 37% along our elevational gradient and, as expected, plants emerged, reached first flower and made their first seed in 41% fewer growing degree days under shorter growing seasons. Although reciprocal transplants revealed modest genetic differentiation across elevation, trait clines were primarily due to striking co-gradient plasticity that paralleled genetic differentiation. Co-gradient plasticity likely evolved in response to considerable interannual variation in season length across our elevational transect, and should prepare R. minor to make adaptive changes to phenology in response to ongoing climate change predicted for montane environments. This article is protected by copyright. All rights reserved.