BOYD, AMY E. Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721. - Geographic variation in morphology and pollinator taxa in Macromeria viridiflora.
Macromeria viridiflora (Boraginaceae), a perennial species that
occurs as isolated populations on the Sky Islands of southwestern
North America, displays geographic variation in floral morphology that
may be related to pollinator variation. Analysis of morphometric data
from eight sites across the range of the species shows significant
among-population variation in 19 out of 20 vegetative and floral
traits measured. Flower size variation is particularly strong and
follows a latitudinal cline, with flowers being much larger in the
southern part of the range and smaller in the northern part of the
range. Observations also indicate differences in floral visitors
between northern and southern populations. While flowers in all
populations were visited by hummingbirds, the large-bodied
hummingbirds visiting plants in the southern regions are not present
in the northern regions, where flowers are visited by hummingbirds
with nearly half the body size and much shorter bills. This
difference in body size of pollinators mirrors the geographic
variation in flower size in M. viridiflora, suggesting that
pollinator-mediated selection may be acting upon the species. Floral
variation will also be placed into a phylogenetic context to determine
the historical direction of change in flower size.
Key words: geographic variation, Macromeria viridiflora, morphometrics, pollinator-mediated selection, sky islands