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AOBPreview originally published online on August 8, 2009
Annals of Botany 2009 104(5):897-912; doi:10.1093/aob/mcp191
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© The Author 2009. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

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

Andreas Jürgens1,*, Simone R. Bosch2, Antonio C. Webber3, Taina Witt1, Dawn Frame4 and Gerhard Gottsberger2

1 School of Biological and Conservation Sciences, University of KwaZulu-Natal, P. Bag X01 Scottsville, Pietermaritzburg 3209, South Africa
2 Botanischer Garten und Herbarium, Universität Ulm, Hans-Krebs-Weg, D-89081 Ulm, Germany
3 Departamento de Biologia – ICB, Universidade Federal do Amazonas, Estrado do Contorno 3000, BR-69077-000 Manaus, AM, Brazil
4 IRD, UMR AMAP, Montpellier, F-34398 France

* For correspondence. E-mail juergensa{at}ukzn.ac.za

Received: 2 April 2009    Returned for revision: 4 June 2009    Accepted: 1 July 2009    Published electronically: 8 August 2009

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.

Key words: Eulophia alta, Orchidaceae, floral biology, floral volatiles, GC-MS, nectar composition, pollinator performance, reproductive success


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