Solidago altissima differs with respect to ploidy frequency and clinal variation across the prairie-forest biome border in Minnesota.
OBJECTIVE
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 Solidago altissima spanning the prairie-forest ecotone in Minnesota in a common garden with a watering treatment. We assessed ploidy frequencies and measured survival, flowering phenology, and plant architectural traits for 4 years.


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 timing of flowering of the cytotypes overlapped in populations sampled from the northeastern hemiboreal forest but differed significantly between cytotypes sampled from populations in the southwestern prairie. The watering treatments had weak effects, and there were no ploidy differences for phenotypic plasticity.


CONCLUSIONS
Our data show that diploids have diverged genetically to a greater extent than polyploids along the environmental clines sampled in this study. Moreover, different environments favor phenotypic convergence over divergence among cytotypes for some traits. Differences in ploidy frequency and phenotypic divergence among cytotypes across gradients of temperature and precipitation are important considerations for restoration in an age of climate change.
Department of Biology, University of Minnesota Duluth, 207A Swenson Science Building, Duluth, Minnesota 55812 USA jetterso@d.umn.edu.
Julie R
JR
Etterson
Department of Biology, University of Minnesota Duluth, 207A Swenson Science Building, Duluth, Minnesota 55812 USA.
Rachel H
RH
Toczydlowski
Department of Biology, University of Minnesota Duluth, 207A Swenson Science Building, Duluth, Minnesota 55812 USA.
Katharine J
KJ
Winkler
Department of Biology, University of Minnesota Duluth, 207A Swenson Science Building, Duluth, Minnesota 55812 USA.
Jessica A
JA
Kirschbaum
Department of Biology, University of Minnesota Duluth, 207A Swenson Science Building, Duluth, Minnesota 55812 USA.
Tim S
TS
McAulay
D057231:Climate Change; D065928:Forests; D014644:Genetic Variation; D018745:Genome, Plant; D065948:Grassland; D008910:Minnesota; D011003:Ploidies; D011891:Rain; D012914:Snow; D036624:Solidago / Q000235:genetics*; D013696:Temperature
Asteraceae; clinal variation; environmental gradient; flowering phenology; genetic differentiation; latitude; longitude; polyploidy