The evolution of pollination systems in Ceropegia

Ceropegia (Apocynaceae subfamily Asclepiadoideae) is a large, Old World genus of more than 180 spp., all of which possess distinctive flask-shaped flowers that temporarily trap pollinators. Using a cpDNA-nrDNA molecular phylogeny of the genus, the taxonomic diversity of pollinators, biogeographic and phylogenetic patterns of pollinator exploitation, and the level of specificity of interactions were assessed for c. 60 Ceropegia taxa. Ceropegia spp. interact with flower visiting Diptera from at least 26 genera in 20 families, of which 11 genera and 11 families are known to be pollinators. Pollinating flies were overwhelmingly (c. 94%) female, presumably seeking oviposition sites, and ranged in size from 0.5 to 4.0 mm. The basal-most Ceropegia clade interacts with the highest diversity of Diptera families and genera, compared with the more derived clades. 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. The genus Ceropegia has largely radiated without evolutionary shifts in pollinator functional specialization, maintaining its interactions with small Diptera. The evolution of pollination systems has been studied from a molecular phylogenetic perspective in few large plant genera, most of which have exploited relatively large, charismatic pollinators such as bees, moths and birds. This study of Ceropegia (Ollerton et al. 2009. Annals of Botany 103: 1501-1514) therefore extends our understanding of the biodiversity of pollination systems into a previously neglected area