Nuances of floral mimicry in Queen of Sheba orchids.

Background and aims: Floral deception can range from finely tuned mimicry of specific rewarding plants (Batesian mimicry) to a general resemblance of the rewarding community (generalized food deception). We focused on two species in the deceptive Thelymitra variegata complex (Queen of Sheba orchids) to examine whether pollination is consistent with generalized food deception or with specific mimicry of co-flowering buzz-pollinated tinsel lilies (Calectasia spp.).

Methods: We assessed (1) overlap in flower colour and scent between orchids, tinsel lilies and other flowers in the rewarding community and (2) pollinator sharing between orchids, tinsel lilies and other species, and (3) quantified orchid reproductive success in relation to abundance of tinsel lilies and other rewarding species.

Key results: We found that Thelymitra speciosa matches the flower colour and scent of its co-flowering tinsel lily, Calectasia gracilis, while Thelymitra porphyrosticta partly overlaps with co-flowering Calectasia demarzii in both traits. The orchids and tinsel lilies shared flower visitors, and the only visitor observed to transfer orchid pollen was the bee Anthoglossa plumata (Colletidae), which displayed a behaviour associated with buzz-pollination. This species was also observed to buzz-pollinate tinsel lilies. In T. speciosa, fruit production increased with abundance of both tinsel lilies and other rewarding species with similar flower colour, suggesting a combination of mimicry and magnet effects. However, relationships were driven by a single population. There was no association between rewarding community and reproductive success in T. porphyrosticta.

Conclusions: The results are partly consistent with mimicry towards the co-flowering tinsel lily for both orchids. Specific mimicry is strongly supported by a close resemblance involving multiple floral traits, and by bee behaviour associated with the buzz-pollinated model. However, this contrasts with the lack of consistent effects of tinsel lily abundance on orchid reproductive success. The findings further suggest that shared floral scent may reinforce visual similarity and highlight that scent may be important in food mimicry systems. Overall, the T. variegata complex offers an interesting system for studying the evolution of mimicry, in particular regarding the contribution of visual and olfactory signals in food mimicry systems.