The Evolution and Maintenance of Mixed Mating Systems
Brunet, Johanne , Sweet, Heather .
The maintenance of a mixed mating system in the rocky mountain columbine: is it adaptive?
Mixed mating system, where both selfing and outcrossing occur in a population, is a common feature of the rocky mountain columbine, Aquilegia coerulea, where outcrossing rates vary between 0.41 and 0.93 among populations. We examined whether the maintenance of selfing in these populations is adaptive or a mere consequence of adaptations for cross-pollination when plants open more than one flower simultaneously. First, we quantified reproductive assurance by measuring the seed set attributed to autogamy in one population. Second, we measured the genetic contribution of autogamous and geitonogamous selfing to the selfing rate. Third, we examined the impact of ecological (pollinators, population size) and morphological factors (floral display size, herkogamy) on outcrossing rate in A. coerulea populations. Seed set was greater in control relative to emasculated flowers suggesting reproductive assurance. However, geitonogamy contributed the majority of selfing in the population the level of autogamous selfing was negligible. The discrepancy between the seed set and genetic data could be explained by preference of bumble bees for control flowers. These data warn against attributing the increase seed set of control flowers to autogamy and reproductive assurance without supporting evidence for equal visitation to both flower types. Hawkmoth abundance and floral display size explained 87 % of the variation in outcrossing rate among populations. None of the other morphological and ecological factors had a direct impact on outcrossing rate. Both hawkmoth abundance and floral display size influenced outcrossing rate via their impact on geitonogamy. Thus, variation in geitonogamous selfing could explain the variation in outcrossing rate and the maintenance of mixed mating system in A. coerulea. Geitonogamy is usually viewed as disadvantageous and an unavoidable consequence of cross-pollination in a plant with more than one flower opened simultaneously. Thus the maintenance of selfing in A. coerulea may require no adaptive explanation.
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1 - USDA-ARS, University of Wisconsin, Department of Horticulture, 1575 Linden Drive, Madison, Wisconsin, 53706, USA
2 - Oregon State University, Department of Botany & Plant Pathology, 2082 Cordley Hall, Corvallis, Oregon, 97331-2902, USA
mixed mating system
floral display size.
Presentation Type: Symposium or Colloquium Presentation
Location: Stevens 5/Hilton
Date: Monday, July 9th, 2007
Time: 10:45 AM