Breaking the rules: discovery of sexual deception in Caladenia abbreviata (Orchidaceae), a species with brightly coloured flowers and a non-insectiform labellum

Abstract

Caladenia is exceptional among orchid genera in that it contains both species pollinated by sexual deception and species pollinated by food-foraging insects. Whereas pollination strategies have been elucidated in some species complexes, others groups have received limited attention, hampering our ability to understand the evolution of the exceptional diversity of species and floral traits in Caladenia. Here, we conducted the first detailed pollination study of a member of the Caladenia filamentosa complex. On the basis of the brightly coloured and scented flowers exhibited by many species, it has been assumed that most members of the group are food-deceptive. However, we show that Caladenia abbreviata Hopper & A.P.Br. is pollinated by an undescribed species of Rhytidothynnus thynnine wasp via sexual deception. Floral dissections showed that the terminal glands on the sepals and petals are the primary source of the sexual attractant, supporting observations from intact flowers that pollinators frequently copulate with these floral parts. Interestingly, contact with the reproductive structures of the plant was not associated with attempted copulation. Our findings highlighted that sexual deception can evolve in lineages without dull-coloured flowers and insectiform labellum structures. Given that the orchid is apparently dependent on a single pollinator species, efforts to conserve this rare species will be dependent on the availability of the pollinator in suitable orchid habitat.