Pollination of flowers by flies (the insect order Diptera) has long fascinated me, in part because it often subverts the idea of what “normal” flowers should look like, but also because it is much less well studied, and appreciated, compared to bee pollination. This is despite the fact that fly pollinated flowers are at least as frequent as bee pollinated flowers in many plant communities, as I show in a forthcoming review in the journal Annual Review of Ecology, Evolution and Systematics (more on that in November when it’s published).
Over the past decade I’ve been studying the large plant genus Ceropegia in the family Apocynaceae (subfamily Asclepiadoideae). The flowers of these species temporarily trap their fly pollinators, releasing them after a period, during which pollination takes place and/or pollen is picked up. The latest study from this work has just been published in the journal Flora, in collaboration with colleagues from eight different countries. The title is:
If you follow that link you can download the PDF for free for the next 50 days.
One of the main findings from this new study is that the diversity of fly families that pollinate Ceropegia spp. is much greater than we had previously realised. The total now stands at 16 different families, including some that rarely, if ever, pollinate other plants (as far as we yet know).
Another important finding is that this clade, which may contain as many as 1000 species in total, seems to have diversified despite that fact that all species are apparently fly pollinated. This is unusual: diversification of plant clades often involves shifts to very different groups of pollinators, e.g. bee to bird or bat pollination.
There’s still lots to discover about this group of plants and this is just the latest output from what is an ongoing project focused on Ceropegia and the Apocynaceae more generally.
Here’s the abstract:
“Pollination by flies (Diptera) has been important to the diversification and ecology of the flowering plants, but is poorly understood in contrast to pollination by other groups such as bees, butterflies and birds. Within the Apocynaceae the genera Ceropegia and Riocreuxia temporarily trap flies, releasing them after a fixed, species-specific period of time, during which pollination and/or pollen removal occurs. This “trap flower” pollination system shows convergent evolution with unrelated species in other families and fascinated Stefan Vogel for much of his career, leading to ground-breaking work on floral function in Ceropegia (Apocynaceae). In this new study we extend the work of the latest broad analysis published by some of the authors (Ollerton et al., 2009 − Annals of Botany). This incorporates previously unpublished data from India and Africa, as well as recently published information, on the diversity of pollinators exploited by Ceropegia. The analyses are based on a more accurate phylogenetic understanding of the relationships between the major groups, and significantly widens the biogeographic scope of our understanding of fly pollination within Ceropegia. Information about the pollinators of 69 taxa (species, subspecies and natural varieties) of Ceropegia is now available. Twenty five families of Diptera are known to visit the flowers of Ceropegia, of which sixteen are confirmed as pollinators. Most taxa are pollinated by species from a single family. Overall, there were no major biogeographic differences in the types of Diptera that were used in particular regions, though some subtle differences were apparent. Likewise there were no differences between the two major clades of Ceropegia, but clear differences when comparing the range of Diptera exploited by Ceropegia with that of the stapeliads. This clade, one of the largest in the Asclepiadoideae, is a fascinating example of a species radiation driven by an apparently relatively uniform set of pollinators.”
Photo credit: flies on flowers of Ceropegia arabica in cultivation by Sage Reynolds.