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Patterns of selection vary with resources and differ between sex-functions in Platanthera bifolia (Orchidaceae)
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Faculty of Science and Technology, Biology, Department of Evolutionary Biology.
Manuscript (Other academic)
URN: urn:nbn:se:uu:diva-89659OAI: oai:DiVA.org:uu-89659DiVA: diva2:161326
Available from: 2002-02-13 Created: 2002-02-13 Last updated: 2010-01-13Bibliographically approved
In thesis
1. Selection and Floral Evolution in Platanthera bifolia and P. chlorantha (Orchidaceae)
Open this publication in new window or tab >>Selection and Floral Evolution in Platanthera bifolia and P. chlorantha (Orchidaceae)
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Natural selection mediated by pollinators has influenced the evolution of floral diversity of the flowering plants (angiosperms). The scope of this thesis was to study: 1) phenotypic selection, 2) mating systems, and 3) floral shifts involved in plant speciation. Model plant species were Platanthera bifolia and P. chlorantha (Orchidaceae). These orchids are moth-pollinated, strictly co-sexual (bisexual flowers), and produce a spike that displays 10-20 white flowers.

I explored the influence of characters on plant fitness by using multiple linear regressions. Pollen removal (male fitness) and fruit set (female fitness) increased with more flowers per plant in three P. bifolia populations. There was selection towards longer spurs in a dry year when average spur length was shorter than in normal-wet years. Female function was sensitive to drought, which enabled an application of the male function hypothesis of floral evolution (Bateman's principle). The results show that selection may vary between populations, years, and sex-functions.

I examined inbreeding by estimating levels of geitonogamy (self-pollination between flowers of an individual) with an emasculation method in two P. bifolia populations. Geitonogamy did not vary with inflorescence size. Levels of geitonogamy was 20-40% in the smaller, but non-significant in the larger population. This may relate to lower number of possible mates and pollinator activity in the smaller population.

Platanthera bifolia exhibits the ancestral character state of tongue-attachment of pollinia on the pollinator. Its close relative P. chlorantha attaches its pollinia onto the pollinator's eyes. To explore the mechanism of a floral shift, pollination efficiency and speed was compared between the two species. The results showed no differences in pollination efficiency, but P. chlorantha had faster pollen export and import. Efficiency of pollination in terms of speed may cause floral shifts, and thus speciation.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2002. 26 p.
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 685
Developmental biology, Evolution, phenotypic selection, male function hypothesis, mating systems, floral shifts, orchids, pollination, moth pollinators, Platanthera., Utvecklingsbiologi
National Category
Developmental Biology
Research subject
Systematic Botany
urn:nbn:se:uu:diva-1754 (URN)91-554-5226-4 (ISBN)
Public defence
2002-03-08, Lindahl Hall, Norbyvägen 18A, Uppsala, 10:00
Available from: 2002-02-13 Created: 2002-02-13Bibliographically approved

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