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Despite their apparent integration, spur length but not perianth size affects reproductive success in the moth-pollinated orchid Platanthera bifolia
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Ecological Botany.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Ecological Botany.
2009 (English)In: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 23, no 5, 1022-1028 p.Article in journal (Refereed) Published
Abstract [en]

The evolution of many floral traits is thought to have been shaped  by pollinator-mediated selection for increased attractiveness or an   improved mechanical fit of flowers to pollinators. Yet, few studies have examined experimentally the independent and interactive effects of   different aspects of flower morphology on plant reproductive success.   In the orchid Platanthera bifolia, perianth size and spur length are   positively correlated within and among populations. To test the hypothesis that pollination success and seed output increases with   increasing perianth size and spur length, we manipulated the two traits   in a factorial design in a long-spurred population of P. bifolia   pollinated by long-tongued hawkmoths. Additionally, to determine   whether differences in selfing rate can explain variation in fruit set   and fruit size, we performed controlled self- and cross-pollination.   Plants with long spurs had more flowers pollinated, more pollen removed   and produced more and larger fruits compared to plants with short   spurs. In contrast, perianth size did not affect the pollination   success or fruit production of P. bifolia.   Fruit production and fruit size did not differ among flowers pollinated   with self- and cross pollen, respectively. This indicates that reduced   pollen deposition rather than pollinator-mediated self-pollination   caused the reduction in fruit set and fruit volume observed after   shortening of the spur.   The results demonstrate that spur length, but not perianth size, is   critical for reproductive success in P. bifolia, and suggest that   among-population differentiation in perianth size may reflect a  correlated response to selection on spur length. The results are  consistent with the hypothesis that visual display is less important   than other cues for the reproductive success of P. bifolia, and   underscore the necessity to experimentally examine the functional   significance of putatively adaptive traits.

Place, publisher, year, edition, pages
2009. Vol. 23, no 5, 1022-1028 p.
Keyword [en]
pollination success, seed output, floral evolution, floral display, flower morphology, pollen removal
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:uu:diva-108552DOI: 10.1111/j.1365-2435.2009.01595.xISI: 000269976800020OAI: oai:DiVA.org:uu-108552DiVA: diva2:236285
Available from: 2009-09-22 Created: 2009-09-22 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Evolution of Spur Length in a Moth-pollinated Orchid
Open this publication in new window or tab >>Evolution of Spur Length in a Moth-pollinated Orchid
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

There is considerable evidence that pollinator shifts can explain many differences in flower morphology between closely related plant species, but the extent to which pollinator shifts can explain the maintenance of among-population variation in floral traits within species is poorly known. In this thesis, I combined comparative and experimental approaches to examine the evolution of floral traits in the moth-pollinated orchid Platanthera bifolia. More specifically, I investigated (1) the relationship between flower and pollinator morphology, (2) phenotypic selection on morphology and phenology in populations in contrasting environments, (3) components of prezygotic reproductive isolation among divergent populations, and (4) the adaptive and functional significance of two correlated floral traits.

A study of Scandinavian of P. bifolia populations revealed that spur length was positively correlated with proboscis length of local pollinators, which suggests that variation in spur length reflects adaptive evolution in response to geographically variable pollinator-mediated selection.

A phenotypic selection study on Öland, SE Sweden, suggested that disruptive selection on spur length contributes to the maintenance of a bimodal distribution of spur length in mixed habitats, but provided very limited evidence of divergent selection on plant morphology and flowering phenology in grassland and woodland habitats.

Field experiments revealed strong reproductive isolation between divergent populations on Öland, due to differences in spatial distribution, flowering phenology, and pollinators, and among-population incompatibility. The results suggest that prezygotic reproductive isolation contributes to the maintenance of population differentiation in floral traits in P. bifolia.

A field manipulation experiment demonstrated that spur length but not perianth size affects pollination success and seed production. This suggests that among-population differentiation in perianth size may be the result of a genetic correlation with spur length.

Taken together, the results of this thesis suggest that pollinator-mediated selection can shape the evolution of intraspecific floral variation.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 33 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 712
Keyword
Platanthera bifolia, floral evolution, natural selection, pollination, spur length, population differentiation, divergent selection, disruptive selection, reproductive isolation
National Category
Biological Sciences
Research subject
Ecological Botany
Identifiers
urn:nbn:se:uu:diva-113086 (URN)978-91-554-7714-1 (ISBN)
Public defence
2010-03-05, Zootissalen, Villavägen 9, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2010-02-12 Created: 2010-01-25 Last updated: 2011-02-09Bibliographically approved

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