Comparative Pollen and Dye Transfer by Pollinators of Delphinium nelsonii

The perennial herb Delphinium nelsonii Greene is pollinated by hummingbirds and bumble-bees in Colorado, USA. Birds and bees were induced to forage in an aviary and the resulting carryover of pollen and fluorescent dye powder from an initial male-phase donor flower to emasculated female-phase recipients was compared. Bumble-bee visitation caused dye transfer whose properites closely resembled those of pollen transfer on average, while hummingbird visitation caused more variable deposition of dye and pollen on recipients and longer distances of pollen than of dye movement on average. The last result implies that pollen dispersal and genetic neighbourhood area are more extensive than estimated previously from dye dispersal in D. nelsonii populations. Pollen transfer in this species also is comparable to that in two sympatric herbs, Ipomopsis aggregata (Pursh) V. Grant and Erythronium grandiflorum Pursh. Key-words: Bumble-bees, Colorado, Delphinium, genetic neighbourhood, hummingbirds, pollination, pollen dispersal