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- Maad, Johanne, et al.
(författare)
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Incidence of geitonogamy differs between two populations in the hawkmoth-pollinated Platanthera bifolia (Orchidaceae)
- 2004
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Ingår i: Canadian Journal of Botany. - 0008-4026. ; 82:11, s. 1586-1593
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Tidskriftsartikel (refereegranskat)abstract
- We estimated geitonogamy in individuals with different inflorescence sizes in a small (100-200 flowering individuals) and a large population (>700 flowering individuals) of the self-compatible, moth-pollinated orchid Platanthera bifolia (L.) L. C. Rich. (Orchidaceae). Geitonogamy was estimated as the percent reduction in pollen receipt by emasculated compared with control plants over seven nights. Geitonogamy in the small population was 23% and 38% during 2 years, respectively. In contrast, no geitonogamy was detected during a single flowering season in the large population. Geitonogamy did not vary with inflorescence size and emasculation had no impact on fruit set. The difference in geitonogamy between the populations in the present study may be related to pollinator abundance and behaviour. We suggest that incidence of geitonogamy will be higher if the pollinator carries smaller pollen loads when arriving at a plant because there will be a smaller fraction of cross-pollen carried after visiting one flower. Geitonogamy may be influenced by available number of mates, pollen load size, pollinator behaviour, and pollen carryover.
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- Maad, Johanne, et al.
(författare)
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On the mechanism of floral shifts in speciation: gained pollination efficiency from tongue- to eye-attachment of pollinia in Platanthera (Orchidaceae)
- 2004
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Ingår i: Biological Journal of the Linnean Society. ; 83:4, s. 481-495
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Tidskriftsartikel (refereegranskat)abstract
- This work explores the mechanism of floral shifts that may result in speciation. The model organisms chosen were the moth-pollinated pollinator-limited orchid species Platanthera bifolia and P. chlorantha. P. bifolia exhibits tongue-attachment of pollinia on pollinators, a character state that has been found previously to be ancestral. The close relative P. chlorantha exhibits the derived state of eye-attachment of pollinia on pollinators. We reasoned that differences between the species in pollination efficiency could give insights into the mechanism of floral shifts and thus cladogenesis. Four populations per species were investigated. In three populations, where the species were growing intermixed and were sharing pollinators, there was significant difference in the pollen export and import efficiency per visit-night (night with pollen export and/or import) between the two species. P. bifolia exported pollinia more efficiently but imported pollen less efficiently than did P. chlorantha. Pollen import was 1.74 times faster in P. chlorantha (eye-attachment) than it was in P. bifolia (tongue-attachment). P. chlorantha had a lower risk of interference between pollen import and export. An increase in fitness through greater speed and efficiency of pollen import due to an enlargement of the stigmatic surface and a reduction in the risk of sexual interference may therefore be mechanisms of the floral shift from tongue- to eye-attachment of pollinia on pollinators.
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- Maad, Johanne, 1970-
(författare)
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Selection and Floral Evolution in Platanthera bifolia and P. chlorantha (Orchidaceae)
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 8. |
- Maad, Johanne, et al.
(författare)
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Variable selection in Platanthera bifolia (Orchidaceae): phenotypic selection differed between sex functions in a drought year.
- 2004
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Ingår i: J Evol Biol. ; 17:3, s. 642-650
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Tidskriftsartikel (refereegranskat)abstract
- We estimated selection on three morphological characters in the hermaphroditic, hawkmoth-pollinated orchid Platanthera bifolia and explored selection surfaces through male and female function. The work was carried out in northern Sweden during two flowering seasons (1994 and 1995) in one natural population and one season (1995) in another natural population. Fitness was estimated as number of pollinia removed (male function) and number of fruits produced (female function). We detected directional selection towards larger inflorescence size (flower number) through both sex functions in both populations in 1995. In 1994, with an unusually dry growing season, 78% of the individuals failed to set any fruit, and there was selection for larger inflorescences only through male function. In this year, there was selection towards longer flower spurs, which could be a direct or indirect effect of spurs being shortened by drought. The results demonstrate that selection patterns may vary temporally and spatially, and that the 'male function hypothesis' may be applicable as female function is more resource dependent than male function.
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