Journal Article

Reproductive biology of <i>Acrolophia cochlearis</i> (Orchidaceae): estimating rates of cross-pollination in epidendroid orchids

Craig I. Peter and Steven D. Johnson

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 104, issue 3, pages 573-581
Published in print August 2009 | ISSN: 0305-7364
Published online November 2008 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcn218
Reproductive biology of Acrolophia cochlearis (Orchidaceae): estimating rates of cross-pollination in epidendroid orchids

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  • Ecology and Conservation
  • Evolutionary Biology
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Background and Aims

Pollen fates strongly influence mating success in plants but are difficult to quantify. By promoting foraging constancy in pollinators, floral rewards such as nectar may enhance the overall efficiency of pollen transfer. However, this can also lead to high levels of geitonogamy. Pollen fates were studied in Acrolophia cochlearis, a member of a terrestrial epidendroid orchid genus that includes both rewarding and deceptive species.

Methods

Pollinator observations were conducted. Pollen transfer efficiency (PTE), the proportion of removed pollinia deposited on stigmas, was measured in a large population at regular intervals throughout the 5-month flowering season. The level of cross-pollination in two populations was estimated from the percentage of seeds with embryos in naturally pollinated fruits.

Key Results

Acrolophia cochlearis (and a congener A. micrantha) produce minute but concentrated nectar rewards. Observations showed that A. cochlearis is pollinated exclusively by a solitary bee species, Colletes claripes. Although both sexes visited flowers, only males carried pollinaria. Overall levels of pollination and PTE of the rewarding A. cochlearis were much higher than in a deceptive congener, A. capensis. Seeds resulting from self-fertilization had a significantly lower probability of containing viable embryos than did those from cross-fertilization. This dichotomy in fruit quality was used to estimate that cross-pollination occurred in approx. 66 % of A. cochlearis flowers in a large dense population and approx. 10 % in a small sparse population. Traits of A. cochlearis that limit geitonogamy include pollinarium reconfiguration that exceeds the visit time of pollinators and rapid flower senescence following visitation.

Conclusions

Presence of a nectar reward in Acrolophia cochlearis results in high levels of PTE. It is estimated that approx. 33–90 % of fruits in natural populations arise from self-pollination in this species.

Keywords: Reward; deception; pollen transfer efficiency; pollen tracking; geitonogamy; Acrolophia cochlearis; epidendroid orchid; Cape floral region

Journal Article.  5238 words.  Illustrated.

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

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