Solidago altissimadiffers with respect to ploidy frequency and clinal variation across the prairie-forest biome border in minnesota

PREMISE OF THE STUDY: Although our awareness of ploidy diversity has expanded with the application of flow cytometry, we still know little about the extent to which cytotypes within mixed-ploidy populations are genetically differentiated across environmental gradients. METHODS: To address this issue, we reared 14 populations of S olidago altissimaspanningthe prairie–forest ecotone in Minnesotain acommon garden with awateringtreatment. We assessed ploidy frequencies and measured survival, floweringphenology, and plant architectural traits for 4 years. KEY RESULTS: All populations harbored multiple cytotypes; prairie populations were dominated by tetraploids, forest populations by hexaploids. Diploids and polyploids differed significantly for 84% of the traits. Beyond average differences, the slope of trait values covaried with latitude and longitude, but this relationship was stronger for diploids than the other two polyploid cytotypes as indicated by numerous ploidy × latitude and ploidy × longitude interactions. For example, the timingof floweringof the cytotypes overlapped in populations sampled from the northeastern hemiboreal forest but differed significantly between cytotypes sampled from populations in the southwestern prairie. The wateringtreatments had weak effects, and there were no ploidy differences for phenotypicplasticity. CONCLUSIONS: Our datashow that diploids have diverged genetically to agreater extent than polyploids alongthe environmental clines sampled in this study. Moreover, different environments favor phenotypicconvergence over divergence amongcytotypes for some traits. Differences in ploidy frequency and phenotypicdivergence amongcytotypes across gradients of temperature and precipitation are important considerations for restoration in an age of climate change.