Journal Article

Pollination function transferred: modified tepals of <i>Albuca</i> (Hyacinthaceae) serve as secondary stigmas

Steven D. Johnson, Andreas Jürgens and Michael Kuhlmann

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 110, issue 3, pages 565-572
Published in print August 2012 | ISSN: 0305-7364
Published online May 2012 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcs114
Pollination function transferred: modified tepals of Albuca (Hyacinthaceae) serve as secondary stigmas

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  • Evolutionary Biology
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Background and Aims

The stigma, a structure which serves as a site for pollen receipt and germination, has been assumed to have evolved once, as a modification of carpels, in early angiosperms. Here it is shown that a functional stigma has evolved secondarily from modified tepals in some Albuca species (Hyacinthaceae).

Methods

Deposition of pollen on Albuca floral organs by bees was recorded. Pollen germination and fruit set was measured in flowers that had pollen deposited solely on their tepals or had their tepal tips experimentally isolated or removed after pollination.

Key Results

Leafcutter bees deposit pollen onto the papillate apices of the inner tepals of Albuca flowers. Pollen germinates in tepal-derived fluid secreted 2 or 3 d after anthesis and pollen tubes subsequently penetrate the style during flower wilting. Application of cross-pollen to the inner tepal apices of A. setosa flowers led to high fruit set. No fruits were produced in pollinated flowers in which the inner tepals were mechanically isolated or removed.

Conclusions

Pollen capture by tepals in the Albuca clade probably evolved in response to selection for floral morphology that maximizes the accuracy of pollen transfer. These findings show how pollination function can be transferred among floral organs, and shed light on how the original angiosperm stigma developed from sporophylls.

Keywords: Hyacinthaceae; Ornithogaloideae; pollen; pollen germination; pollen receipt; pollen tube; pollination; sexual interference

Journal Article.  5154 words.  Illustrated.

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

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