HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (17) Citing Articles via Google Scholar Google Scholar Articles by Wolf, P. G. Articles by Archibald, J. K. Search for Related Content PubMed PubMed Citation Articles by Wolf, P. G. Articles by Archibald, J. K. Agricola Articles by Wolf, P. G. Articles by Archibald, J. K.

Tests of pre- and postpollination barriers to hybridization between sympatric species of Ipomopsis (Polemoniaceae)¹

² Ecology Center, Utah State University, Logan, Utah 84322 USA; ³ Department of Biology, Utah State University, Logan, Utah 84322 USA; ⁴ Rocky Mountain Biological Laboratory, Crested Butte, Colorado 81224 USA; ⁵ Department of Ecology and Evolutionary Biology, University of California, Irvine, California 92717 USA; ⁶ Department of Biology, University of California, Riverside, California 92521 USA; ⁷ Department of Evolution, Ecology, and Organismal Biology, Ohio State University, 1735 Neil Avenue, Columbus, Ohio 43210 USA

The Ipomopsis aggregata species complex (Polemoniaceae) includes species pairs that hybridize readily in nature as well as pairs that meet along contact zones with no apparent hybridization. Artificial hybrids can be made between I. aggregata and I. arizonica, yet morphological intermediates between these two species have not been observed in natural populations. This apparent lack of hybridization is perplexing given that plants of the two species often grow within a few metres of each other and both species have red flowers visited by the same species of hummingbirds. We used trained hummingbirds to examine pollen transfer within and between species. We also hand-pollinated flowers to examine paternal success of heterospecific and conspecific pollen, testing paternity with electrophoretic examination of seeds. Hummingbirds were not simply better at transferring pollen within than between species. Instead, I. arizonica was a better pollen donor so that considerable pollen transfer was observed from I. arizonica to I. aggregata, but very little in the opposite direction. Conversely, once pollen arrived at stigmas, I. arizonica pollen performed very poorly on I. aggregata pistils. However, pollen from I. aggregata could, in some cases, sire seeds on I. arizonica. We hypothesize that hybrids are scarce in nature, in part, because of asymmetric barriers to reproduction: little pollen transfer in one direction and poor pollen performance in the other.

Key Words: hummingbird • hybrid zone • pollination • reproductive isolation

This article has been cited by other articles:

				D. A. Tierney and G. M. Wardle The relative fitness of parental and hybrid Kunzea (Myrtaceae): The interaction of reproductive traits and ecological selection Am. J. Botany, February 1, 2008; 95(2): 146 - 155. [Abstract] [Full Text] [PDF]

				J. B. Pascarella Mechanisms of prezygotic reproductive isolation between two sympatric species, Gelsemium rankinii and G. sempervirens (Gelsemiaceae), in the southeastern United States Am. J. Botany, March 1, 2007; 94(3): 468 - 476. [Abstract] [Full Text] [PDF]

				G. Aldridge and D. R. Campbell Asymmetrical pollen success in Ipomopsis (Polemoniaceae) contact sites Am. J. Botany, June 1, 2006; 93(6): 903 - 909. [Abstract] [Full Text] [PDF]

				M. A. Chapman, D. G. Forbes, and R. J. Abbott Pollen competition among two species of Senecio (Asteraceae) that form a hybrid zone on Mt. Etna, Sicily Am. J. Botany, April 1, 2005; 92(4): 730 - 735. [Abstract] [Full Text] [PDF]