Data from: Geographic variation in pollen color is associated with temperature stress

The evolution of flower color, especially petal pigmentation, has received
substantial attention. Less understood is the evolutionary ecology of
pollen pigmentation though it varies among and within species and its
biochemical properties affect pollen viability.   We characterize
the distribution of pollen color across 24 populations of the North
American herb Campanula americana, and assess the degree to which this
variation is genetically based. We identify abiotic factors that covary
with pollen color and test whether germination of light and dark pollen is
differentially affected by variable temperature and UaV. Pollen color
vaulries from white to deep purple in C. americana and is genetically
determined. There was a longitudinal cline whereby pollen was darkest in
western populations. Accounting for latitudinal variation, western
populations experience elevated temperature and UV irradiance. Germination
of light-colored pollen was reduced by 60% under high temperature, but
dark pollen was unaffected. Exposure to UV reduced germination of light
and dark pollen similarly. The cline in pollen color across the range may
reflect adaptation to heat stress. This study supports thermal tolerance
as a novel function of pollen pigmentation and contributes to growing
evidence that abiotic factors can drive floral diversity.