Journal Article

Pollination biology of <i>Eulophia alta</i> (Orchidaceae) in Amazonia: effects of pollinator composition on reproductive success in different populations

Andreas Jürgens, Simone R. Bosch, Antonio C. Webber, Taina Witt, Dawn Frame and Gerhard Gottsberger

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 104, issue 5, pages 897-912
Published in print October 2009 | ISSN: 0305-7364
Published online August 2009 | e-ISSN: 1095-8290 | DOI: https://dx.doi.org/10.1093/aob/mcp191
Pollination biology of Eulophia alta (Orchidaceae) in Amazonia: effects of pollinator composition on reproductive success in different populations

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  • Ecology and Conservation
  • Evolutionary Biology
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Background and Aims

Spatial variation in pollinator composition and abundance is a well-recognized phenomenon. However, a weakness of many studies claiming specificity of plant–pollinator interactions is that they are often restricted to a single locality. The aim of the present study was to investigate pollinator effectiveness of the different flower visitors to the terrestrial orchid Eulophia alta at three different localities and to analyse whether differences in pollinator abundance and composition effect this plant's reproductive success.

Methods

Natural pollination was observed in vivo, and manipulative experiments were used to study the pollination biology and breeding system of E. alta at three sites near Manaus, Brazil. To gain a better understanding of the underlying mechanisms of pollinator attraction, nectar composition and secretion patterns were also studied, floral scent composition was analysed and a bioassay was conducted.

Key Results

Flower visitors, pollinator composition, pollinia transfer efficiency of particular pollinator species and natural fruit set differed among the investigated populations of E. alta. Flowers were self-compatible, partially autogamous and effectively pollinated by five bee species (four Centris species and Xylocopa muscaria). Visiting insects appeared to imbibe small amounts of hexose-rich nectar. Nectar sugar content was highest on the third day after flower opening. Floral fragrance analyses revealed 42 compounds, of which monoterpenes and benzenoids predominated. A bioassay using floral parts revealed that only floral tissue from the labellum chamber and labellum tip was attractive to flower visitors.

Conclusions

The data suggest that observed differences in reproductive success in the three populations cannot be explained by absolute abundance of pollinators alone. Due to behavioural patterns such as disturbance of effective pollinators on flowers by male Centris varia bees defending territory, pollinia transfer efficiencies of particular pollinator species also vary between study sites and result in differing reproductive success.

Keywords: Eulophia alta; Orchidaceae; floral biology; floral volatiles; GC-MS; nectar composition; pollinator performance; reproductive success

Journal Article.  13029 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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