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Reproductive isolation among divergent populations of 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.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Differentiation in floral traits has been documented between populations in contrasting habitats in several species of flowering plants, but few studies have investigated whether barriers to reproduction contribute to the maintenance of this variation. We investigated components of prezygotic reproductive isolation between short-spurred and long-spurred populations of the moth-pollinated orchid Platanthera bifolia on the island of Öland, SE Sweden. Short-spurred and long-spurred populations were reproductively isolated due to spatial isolation, and differences in flowering time, pollinator morphology and behaviour. The index of reproductive isolation due to pollinators and flowering time was higher for the early-flowering long-spurred plants than it was for the late-flowering short-spurred plants. In addition, we documented a postpollination isolation mechanism manifested as reduced fruit formation in short-spurred plants when pollinated with pollen from long-spurred plants. The results indicate that strong reproductive isolation contribute to the maintenance of population differentiation in morphology and phenology between long-spurred and short-spurred populations of P. bifolia.

Keyword [en]
Reproductive isolation, spur length, population differentiation, speciation
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:uu:diva-113085OAI: oai:DiVA.org:uu-113085DiVA: diva2:289624
Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2011-02-09Bibliographically 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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