An endangered slipper orchid in southwestern China fakes the look and smell of a fungal infection in order to attract one particular pollinator, the flat-footed fly.
Black-brown spots mark the leaves of the orchid, mimicking the diseased look of a plant covered with fungus. The flowers even smell like they are rotting. When a fly lands on the orchid intending to dine on the infected patches, the deceived insect comes away hungry and covered in pollen.
"This is the first time we’ve seen an orchid that uses both its flowers and leaves in the deception," said orchid researcher Peter Bernhardt of Saint Louis University, co-author of a study published April 25 in the Proceedings of the National Academy of Sciences. "And it’s pollinated by a group of insects that have not been associated with flower pollination previously, to the best of our knowledge."
There are many reasons why insects interact with flowers, said Retha Edens-Meier, a biologist at Saint Louis University who was not involved in the study: "They might be searching for food, water, specific chemicals, sex, a place to sleep or even warmth."
Usually the flower-pollinator system involves an exchange of services: The flowers provide something insects need, while the insects help the flowers to reproduce. But Cypripedium, the genus of orchid in the new study, is a group that does not provide any kind of reward to potential pollinators.
Lead study author Zong-Xin Ren of the Chinese Academy of Sciences hiked Yaoshan Mountain in southwestern China every summer for four years, performing fertilization experiments on the orchids, watching them to see what pollinated the flowers, collecting the pollinators, and analyzing the scents given off by the orchids.
Ren and his colleagues found that the flat-footed fly, which feeds on fungus, was the only insect to visit these slipper orchids. "The flies are very rare," said Ren, who was able to catch only five for the study.
When it analyzed the flies, Ren's team found fungal spores on the mouth parts, head, feet and the pads between the claws on the insect’s feet. The flies also had packets of pollen from the slipper orchids on their backs.
The orchid scents Ren collected also contained similar chemicals given off by a species of fungus that produces black spots of mold on the leaves and fruit of infected plants.
"These infectious fungi are usually very specific as to their hosts," said Bernhardt. "It’s unlikely an orchid would pick up a disease that’s hard-wired to attack a bush or another wildflower."
Ren would like to find out why this fungus doesn’t infect the slipper orchids after visits from a fungus spore-covered flat-footed fly. He also plans to further explore the fungus-slipper–orchid-fly web and study how these relationships contribute to the rare status of both the orchid and the fly.
The subtlety of this deceptive pollination strategy surprised botanist Kingsley Dixon of Kings Park and Botanic Garden in West Perth, Australia, who specializes in conserving rare and threatened plants. "To mimic a fungal food resource using leaf pattern, microanatomy and fragrance chemistry is elegant to the point that I think Darwin himself would have a wry smile at the thought that orchids had concocted such a system for pollination," Dixon said.
Images by Zong-Xin Ren: Endangered slipper orchid (left); flat-footed-fly (right).
See Also:
- 4 New Species of Zombifying Ant Fungus Found
- Mosquito-Attacking Fungus Engineered to Block Malaria
- Dung Fungus Provides New Evidence in Mammoth Extinction
- The Magic of Mushroom Spores
Citation: "Flowers of Cypripedium fargesii (Orchidaceae) fool flat-footed flies (Platypezidae) by faking fungus-infected foliage." By Zong-Xin Ren, De-Zhu Li, Peter Bernhardt and Hong Wang. Proceedings of the National Academy of Sciences, early edition.
