Great Basin Naturalist


Red. orange, and yellow morphs of Mimulus verbenaceus and M. cardinalis were field tested for pollinator preferences. The species are closely similar except that M. verbenaceus flowers have partially reflexed corolla lobes, whereas M. cardinalis flowers have fully reflexed corolla lobes. On the basis of over 6000 bumblebee and hummingbird visits, highly significant (p < .001) patterns emerged. Yellow, which is the mutant color morph in both species and is determined by a single pair of genes, was strongly preferred by bumblebees and strongly eskewed by hummingbirds in both species. Orange and, to a lesser extent, red were strongly preferred by hummingbirds but eskewed by bumblebees in both species. Thus, strong, but partial, reproductive isolation was observed between the yellow mutants and the orange- to red-flowered populations from which they were derived. Color—yellow versus orange and red—appeared more important than shape—partially reflexed versus fully reflexed corolla lobes—in determining the preferences of the guild of pollinators in this particular test environment for Mimulus verbenaceus and M. cardinalis.