AOBPreview originally published online on April 1, 2009
Annals of Botany 2009 103(9):1501-1514; doi:10.1093/aob/mcp072
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This article appears in the following Annals of Botany issue: Special Issue: Plant-Pollinator Interactions [View the issue table of contents]
Fly pollination in Ceropegia (Apocynaceae: Asclepiadoideae): biogeographic and phylogenetic perspectives
1 Landscape and Biodiversity Research Group, School of Applied Sciences, University of Northampton, Park Campus, Northampton NN2 7AL, UK
2 East African Herbarium, National Museums of Kenya, Museum Hill Road, PO Box 45166, 00100 Nairobi, Kenya
3 Department of Plant Systematics, University of Bayreuth, 95444 Bayreuth, Germany
4 Zoology Department, University of Cape Town, Private Bag X3, Rondebosch 7701, Cape Town, South Africa
5 FlyEvidence, 2 Newhouse Terrace, Dunbar EH42 1LG, UK
* For correspondence: E-mail jeff.ollerton{at}northampton.ac.uk
Received: 31 October 2008 Returned for revision: 5 January 2009 Accepted: 12 February 2009 Published electronically: 1 April 2009
Background and Aims: Ceropegia (Apocynaceae subfamily Asclepiadoideae) is a large, Old World genus of >180 species, all of which possess distinctive flask-shaped flowers that temporarily trap pollinators. The taxonomic diversity of pollinators, biogeographic and phylogenetic patterns of pollinator exploitation, and the level of specificity of interactions were assessed in order to begin to understand the role of pollinators in promoting diversification within the genus.
Methods: Flower visitor and pollinator data for approx. 60 Ceropegia taxa were analysed with reference to the main centres of diversity of the genus and to a cpDNA–nrDNA molecular phylogeny of the genus.
Key Results: Ceropegia spp. interact with flower-visiting Diptera from at least 26 genera in 20 families, of which 11 genera and 11 families are pollinators. Size range of flies was 0·5–4·0 mm and approx. 94 % were females. Ceropegia from particular regions do not use specific fly genera or families, though Arabian Peninsula species are pollinated by a wider range of Diptera families than those in other regions. The basal-most clade interacts with the highest diversity of Diptera families and genera, largely due to one hyper-generalist taxon, C. aristolochioides subsp. deflersiana. Species in the more-derived clades interact with a smaller diversity of Diptera. Approximately 60 % of taxa are so far recorded as interacting with only a single genus of pollinators, the remaining 40 % being less conservative in their interactions. Ceropegia spp. can therefore be ecological specialists or generalists.
Conclusions: The genus Ceropegia has largely radiated without evolutionary shifts in pollinator functional specialization, maintaining its interactions with small Diptera. Intriguing biogeographic and phylogenetic patterns may reflect processes of regional dispersal, diversification and subsequent specialization onto a narrower range of pollinators, though some of the findings may be caused by inconsistent sampling. Comparisons are made with other plant genera in the Aristolochiaceae and Araceae that have evolved flask-shaped flowers that trap female flies seeking oviposition sites.
Key words: Apocynaceae, Asclepiadoideae, Brachystelma, Ceropegia, Diptera, flower evolution, generalization, mutualism, pollination, Riocreuxia, specialization, Stapeliinae
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