Floral scent and pollinators of Ceropegia trap flowers

Ceropegia L. (Apocynaceae, Asclepiadoideae) comprises more than 200 species, all characterized by complex pitfall flowers. The deceptive flowers are myiophilous and pollinated predominantly by small flies from different families. It has been suggested that floral scent cues, that mimic food sources or oviposition sites, play an important role for attraction of target fly pollinators, and, together with morphological flower traits, explain the high functional specialization in terms of pollination by specific taxa. However, apart from two Ceropegia species, the floral scent composition and the mimicry strategies in this genus are unexplored. We tested for associations between floral scent and insect visitor and pollinator assemblages of 14 Ceropegia species. We also used nrDNA and chloroplast DNA markers to calculate a Maximum Likelihood tree and test for phylogenetic signal in scent chemistry and flower visitors/pollinators. The observed pollinators belonged to eight fly families, at least 18 genera, and 33 morphospecies, but each Ceropegia species was typically associated with only one or two pollinating fly families or genera. We detected a total of 317 floral volatiles, including aliphatic and aromatic components, terpenes, and various unknowns. Both flower visitor and pollinator patterns did not show an overall association with floral
scent chemistry. There was phylogenetic signal in flower visiting fly families and fly pollinator assemblages, but not in flower visiting fly morphospecies and overall scent chemistry. We discuss that despite the not existing correlation between pollinator and scent patterns the highly specific pollination system in Ceropegia will be explained mainly by floral scent chemistry.