AOBPreview originally published online on February 22, 2006
Annals of Botany 2006 97(5):767-777; doi:10.1093/aob/mcl033
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Nectar Sugar Composition and Volumes of 47 Species of Gentianales from a Southern Ecuadorian Montane Forest
Department of Plant Systematics, University of Bayreuth, 95440 Bayreuth, Germany
* E-mail Doris.wolff{at}gmx.de
Received: 7 September 2005 Accepted: 11 January 2006 Published electronically: 22 February 2006
• Background and Aims This study investigates 47 taxonomically related species (Gentianales), all native to a tropical montane forest in southern Ecuador, in terms of nectar chemistry and nectar volumes in relation to pollination biology.
• Methods Nectar volumes of covered (24-h production) and uncovered (standing crop) flowers were measured in the natural habitat. Sucrose, fructose and glucose were quantified in the nectar using high performance liquid chromatography. Flower visitors were observed.
• Key Results Nectar sugar concentration did not differ significantly among the pollination syndromes. Regarding sugar composition, the only significant differences were found in chiropterophilous and myiophilous flowers, which had a significantly lower sugar ratio than sphingophilous flowers. A separation of chiropterophilous and myiophilous flowers from the other pollination syndromes is further substantiated by non-linear multidimensional scaling using the chord-normalized expected species shared index of dissimilarity based on nectar sugar compositions. The matrix test revealed no correlation of observed floral visitors to nectar concentrations; however, a weak significant correlation was found between floral visitors and nectar sugar compositions. The nectar volumes of covered and uncovered flowers are related to, and differ significantly among, pollination syndromes. Matrix tests revealed correlation between floral visitors and nectar volume of covered flowers and, to a lesser extent, of uncovered flowers.
• Conclusions Sucrose is the predominant floral nectar sugar in the order Gentianales, suggesting that nectar sugar composition is a conservative characteristic. However, some degree of an adaptive convergence of floral nectar compositions to principal pollinator type within the constraints set by phylogenetic history is likely. The driving force to visitation appears to be the volume of nectar the visitor can expect to consume.
Key words: Nectar sugar composition, nectar volume, nectar standing crop, pollination syndrome, Rubiaceae, Gentianaceae, tropical montane forest, Ecuador
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