Yang, Ji , Hodges, Scott .
Reproductive isolation and mating patterns within an Aquilegia hybrid zone.
Specialization to different pollinators has been suggested as a major cause of assortative mating between plant species though some studies suggest that hybridization can cause this barrier to reproduction to break down. We directly measured mating patterns in a natural hybrid zone between Aquilegia formosa and A. pubescens using paternity analysis. We found that plants are significantly more likely to mate when they have similar morphology and when they are in close proximity to each other. Matings between the two species were nearly 90 percent less-likely than plants with identical morphology. In particular, we found that similarity between plants in spur length, flower orientation and spur color each significantly increased the probability of mating. These mating patterns can be explained by both pollinator discrimination, hummingbirds preferentially visited shorter spurred and more pendant flowers while hawkmoths preferentially visited longer spurred and more upright flowers, and pollen transfer dynamics caused by the ‘fit’ between pollinator and flower morphology. We also found that intermediate hybrids had somewhat lower outcrossing rates than plants with flowers more similar to parental species. To estimate the overall contribution of pollinator specialization to reproductive isolation we also measured other reproductive barriers. We found that extrinsic selection owing to habitat differences is also an important reproductive isolating barrier between these species. In contrast, we found no evidence of postzygotic intrinsic selection against hybrids. Our results illustrate how changes in flower morphology and their affect on pollinator visitation and pollen transfer can promote speciation.
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1 - University of California Santa Barbara, Ecology Evolution Marine Biology, 3061 Porter St. NW, Washington, DC, 20008, USA
2 - University of California Santa Barbara, Department of Ecology Evolution And Marine Biology, Santa Barbara, California, 93106-9610, USA
Presentation Type: Oral Paper:Papers for Topics
Date: Wednesday, July 30th, 2008
Time: 4:30 PM