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Stigma receptivity and effects of prior self-pollination on seed set in tristylous Lythrum salicaria (Lythraceae)
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
2006 (English)In: American Journal of Botany, Vol. 93, no 1, 142-147 p.Article in journal (Refereed) Published
Abstract [en]

Stigma position is a key aspect of flower morphology that may influence pollination success and seed production. In the self-incompatible, tristylous herb, Lythrum salicaria, the stigma is positioned inside the corolla tube in the short-styled morph, but outside the corolla in the mid- and long-styled morphs. We performed controlled pollinations to determine whether style morphs differ in duration of stigma receptivity and in interference caused by self-pollen deposition. As predicted, flowers of the short-styled morph remained receptive for longer if not pollinated than did flowers of the other two style morphs. When deposition of self-pollen preceded compatible cross-pollination, seed set was higher in the mid-styled morph than in the other style morphs. Interference caused by self-pollen deposition was overall strongest in the short-styled morph, but the magnitude of differences among style morphs was contingent on the relative timing of self and compatible pollen receipt. The results indicate that both differences in duration of stigma receptivity and interference from self-pollen deposition may contribute to observed variation in seed production and pollen limitation among style morphs in natural populations of L. salicaria. An association between stigma position and duration of stigma receptivity should constrain the evolution of flower morphology.

Place, publisher, year, edition, pages
2006. Vol. 93, no 1, 142-147 p.
URN: urn:nbn:se:umu:diva-4646OAI: diva2:143837
Available from: 2005-08-30 Created: 2005-08-30 Last updated: 2009-05-19Bibliographically approved
In thesis
1. Plant-animal interactions and seed output of two insectpollinated herbs
Open this publication in new window or tab >>Plant-animal interactions and seed output of two insectpollinated herbs
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

I combined comparative and experimental studies in the field and in the greenhouse to examine factors influencing reproductive success in two insect-pollinated herbs, the tristylous, selfincompatible perennial Lythrum salicaria and the self-compatible, biennial Pedicularis palustris. More specifically, I explored (i) the effects of plant population characteristics on the intensity and outcome of interactions with pollinators and seed predators, (ii) whether flower morphology affects duration of stigma receptivity, and (iii) whether damage-induced reduction in floral display reduces pollinator visitation and increases pollen limitation.

As predicted, the rate of pollinator visitation tended to increase and the number of flowers probed per plant tended to decrease with increasing population size in L. salicaria, but these relationships only approached statistical significance. By taking advantage of the pollen size polymorphism that is typical of many heterostylous plants, I could show that the number of compatible pollen grains received increased with population size, and that this was associated with a reduction in pollen limitation and increased seed output per flower. The deposition of high numbers of incompatible conspecific and heterospecific pollen grains did not appear to reduce seed set.

In P. palustris, fruit set and seed predation varied markedly among populations and years, but this variation could only partly be explained by variation in population size. Fruit set was positively related to population size, and seed predation was negatively related to population size, in one of three years. Similarly, the level of pollen limitation, which was quantified in two years, varied among populations, but was not related to population size, density or isolation.

In L. salicaria, both the duration of stigma receptivity and the effect of prior self-pollination on seed output varied among style morphs. These differences may contribute to morph-specific differences in pollen limitation and seed production documented in the field.

The results of a field experiment demonstrated that damage to the shoot apex may markedly reduce fruit production in L. salicaria, and suggested that this is mainly because damage reduces flower number. I found no evidence that a reduced floral display increased the severity of pollen limitation.

Taken together, the results show that interactions with both pollinators and herbivores may markedly affect reproductive output in the two plant species, and that the intensity of both mutualistic and antagonistic interactions vary considerably in space and time. Moreover, they are consistent with the hypothesis that pollination success should depend less on population size in selfcompatible than in self-incompatible plants.

Place, publisher, year, edition, pages
Umeå: Ekologi, miljö och geovetenskap, 2005. 23 p.
plant reproduction, pollen limitation, pollinator behaviour, heterostyly, seed predation, Lythrum salicaria, Pedicularis palustris, stigma receptivity, self-pollen
National Category
urn:nbn:se:umu:diva-576 (URN)91-7305-911-0 (ISBN)
Public defence
Available from: 2005-08-30 Created: 2005-08-30Bibliographically approved

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